FTSE 100 picked up into the close to finish around 30 points higher at 7,398.
FTSE 250 also travelled higher, up over 95 points at 20,316.
Traders were buoyed by noises about the City of London, the global financial hub, retaining some benefits after the UK leaves the EU.
Since the vote to leave 22 months ago, powerful finance companies in London have been searching for some way to maintain the existing cross-border trading.
"After spending most the day hugging the flatline, the FTSE finally picked up in the afternoon, lifted higher by continued weakness in the pound versus the mighty dollar and by hopes that the City could retain some benefits post Brexit.
"The FTSE climbed to within a whisker of 7400, a level last seen in early February," said Fiona Cincotta, senior market analyst at City Index.
In the currency markets, the pound added 0.44% against the Euro, and was down 0.36% against the US dollar.
Wealth management groups were atop the blue-chip index, with St James's Place (LON:STJ) up 3.33% to 1,146.50p, Old Mutual (LON:OML) added 2.72% to 249.20p while on the biggest losing front, NMC Health (LON:NMC) was in focus, down 3.47% to stand at 3,560p.
Customers at challenger bank TSB are still experiencing issues accessing their money after a weekend upgrade to its mobile and online banking systems led to a litany of problems.
In a statement, the bank said: "We are currently experiencing large volumes of customers accessing our mobile app and internet banking which is leading to some intermittent issues with people accessing our services,"
"We are really sorry for the inconvenience this is causing our customers and want them to know we are working as hard and as fast as we can to resolve this problem."
I promise to stop complaining soon.
Not yet, though.
@TSB this is ridiculous it's now Monday and I still can't pay my bills cause I can't access my account,
And I will have to pay charges now????
The US composite output index has hit a two-month high of 54.8, driven by above-forecast growth in both services and manufacturing.
Services activity was reported at 54.4, above a forecast of 54.1, while manufacturing registered at 56.5 compared to a forecast of 55.2, both well above the 50 point growth benchmark.
Additionally, a report released by the National Association of Realtors revealed existing home sales in the US increased much more than expected in March.
Sales rose 1.1% in March to an annual rate of 5.6mln, well above economist forecasts of 0.2%, however, they were still down 1.2% compared to the same period a year ago.
IHS Markit US Composite Output Index rises to 54.8 (vs. 54.2 prev) amid fastest growth in new orders since March 2015. Sector level data reveals sharpest expansion in manufacturing sector in 43 months. More here: https://t.co/gbTJj59aZk pic.twitter.com/mohmHbgnit
- Markit Economics (@MarkitEconomics) 23 April 2018The UK Takeover Panel has said SS&C Technologies Inc (NASDAQ:SSNC) has until 5 May to make a firm offer for FTSE 250 software company Fidessa Group PLC (LON:FDSA).
The deadline follows an intense bidding war last week which saw Fidessa reject what was originally thought to be a secure takeover bid by Swiss company Temenos Group in favour of an offer from ION Capital Group which valued the company at around 38p per share.
Temenos has said that it would not raise its own offer before the new deadline.
Fidessa shares were trading down 1.3% at 4,000p in late-afternoon trading.
Cryptocurrency Bitcoin topped US$9,000 on Sunday, as a resurgence in the trading of digital currency continued.
One of the most bullish crypto investors, managing partner at Fundstrat Global Advisors Tom Lee, has pegged the currency with a year-end price target of US$25,000.
In company news, The Co-operative Group's ?140mln proposed takeover of convenience store wholesaler Nisa has been approved by the UK competition watchdog.
The Competition and Markets Authority (CMA) revealed that it will not refer the merger for an in-depth investigation following an initial probe into the deal.
The Co-op swooped in with an offer to buy Nisa in October after rival J Sainsbury (LON:SBRY) shelved plans to acquire the wholesaler.
Existing home sales data will be a major announcement today as US stocks seek to recover from a negative finish last week.
The Dow closed down 0.8% last Friday, with the Nasdaq tumbling 1.3% and the S&P 500 shedding 0.9%.
Most eyes will be on Google's parent company Alphabet Inc. (NASDAQ:GOOG, GOOGL) as it prepares to release its financial results for the first quarter.
In the UK, the FTSE 100 turned green in the early afternoon, up 3.6 points to 7,371.
The chief executive of FTSE 100 conglomerate Whitbread plc (LON:WTB), Alison Brittain, is expected to set out her stance on the group's potential breakup at its full-year results on Wednesday.
According to the Sunday Times, city sources have said Brittain is not "philosophically opposed" to the spin-off of the group's Costa Coffee chain, with it being a case of "when, not if".
In a note to clients, analysts at Liberum said: "We believe Whitbread management are open-minded but believe now is not the time (mid-way through transformation, lacklustre LFL and recent China acquisition) and, in any case, are not thought to have received any offers."
Whitbread shares were up 1% at 4,278p in lunchtime trading.
In other news, Martyn Lewis, the founder of the web site MoneySavingExpert, is to sue Facebook Inc (NASDAQ:FB) for defamation of character.
Lewis claims that the social media site has displayed at least 50 adverts purporting to be endorsed by him but which, in fact, did not have his seal of approval.
The FTSE 100 was relatively stagnant at midday, down 2.2 points at 7,365 as geopolitical issues continued to drive uncertainty.
Meanwhile, the dollar hit a seven-week high as a rise in 10-year treasury yields to almost 3% sent investors rushing toward the greenback.
The rise in yields was driven primarily by inflationary pressures, along with increases in US debt issuance and a reduction in tensions with China and North Korea.
In UK company news, Marks and Spencer Group Plc (LON:MKS) shares gained after Credit Suisse upgraded the stock to 'neutral' from 'underperform' amid signs of a recovery in the UK consumer environment.
The UK retailer, whose clothing division was already struggling, has been hit by a slowdown in consumer spending as higher inflation and stagnant wage growth reduce disposable incomes.
M&S shares were up 0.4% at 281.8p.
Carpetright PLC's (LON:CPR) largest shareholder, Meditor Capital Management, has upped its stake in the struggling retailer to nearly 30% from a previous holding of around 16.4%.
Carpetright previously agreed a loan with Meditor in exchange for new shares to fund the short-term running of the company after a series of profit warnings caused mainly by weak UK retail spending.
Its shares were down 1.3% at 36.5p in late-morning trading.
Elsewhere, oil prices fell slightly after rising US borrowing costs and the prospect of further output rises were bolstered by an increase in the weekly rig count.
Brent crude futures fell 49 cents to US$73.57 a barrel, although underlying sentiment remained bullish, with Ole Hansen of Saxo Bank telling Reuters OPEC may be potentially trying to "overtighten" the market.
City minister John Glen has said the EU has indicated that it is willing to provide some form of access for Britain's financial services following Brexit.
Speaking to the CityWeek conference, Glen said: "The EU have now recognised that there will be some form of market access in financial services having previously dismissed the idea."
He also dismissed talk of a "race to the bottom" in regulation, a move that would make it much harder for Britain to secure access to the EU's financial market.
"We do not intend to rip up the rulebook after Brexit," he said.
Meanwhile, challenger bank TSB has been hit with numerous complaints following an upgrade to its online and mobile banking systems over the weekend.
Complaints included one customer saying he could see other people's accounts, with another reportedly being wrongly credited ?13,000.
Sterling dropped to a two-week low against the dollar to around US$1.40 as investors worried the Bank of England (BoE) could delay an interest rate rise following weaker than expected wage growth and inflation.
Comments by the BoE governor Mark Carney that the data was 'mixed' also piled additional pressure on the pound, which fell 1.7% for the week as investors attempted to price the possibility of a delay to the rate hike.
ING FX analyst Viraj Patel told Reuters that the gross domestic product figures due later this week "may be enough to rekindle market expectations".
However, he cautioned that a cross-party and non-binding technical vote on Brexit on Thursday could impact sterling if it threatened Prime Minister Theresa May's leadership.
The FTSE 100 made a relatively flat start to the day, down 4 points at 7,364 as global markets continued to suffer from uncertainty driven by geopolitical developments.
"Trade tariffs, US sanctions and technology are all having a push and pull effect on equity markets," said Rebecca O'Keeffe, head of investment at Interactive Investor.
"Despite some optimism that the US and China will reach a truce on trade tariffs, investors are not putting out the bunting yet, as discussions between the world's two largest economies are likely to be protracted and the negotiation style of President Trump provocative," she added.
In the FTSE 250, outsourcing group Capita PLC (LON:CPI) saw shares leap 11.3% to 177.9p as it announced plans to raise ?701mln through a rights issue as it unveiled a wider full year loss with investors relieved that the troubled firm could be finding a way out of the mire.
But it was not so good news for fellow FTSE 250 constituent, shipping company Clarkson PLC (LON:CKN), shares in which plummeted 35% to 2,010p after it warned on first half and full year profits due to a challenging trading environment and a fall in the value of the US dollar.
FairFX Group Plc (LON:FFX), the electronic banking and international payments group, has got off to a strong start to 2018 with revenue up 18.7% year-on-year on a like-for-like basis.
Midatech Pharma Plc (LON:MTPH) is "fully focused" on advancing its drug pipeline "into clinical development and beyond", according to chief executive designate, Dr Craig Cook. Positive clinical trial readouts for Q-Octreotide would accelerate the path to product registration, the company said.
Directa Plus Plc (LON:DCTA) is to work with one of Italy's leading re-tread companies to produce better performing tyres for buses and lorries. Marangoni will work with Directa's G+ compound to produce a bespoke product designed for specifically for commercial vehicle re-treads.
Kromek Group PLC (LON:KMK) has been awarded a three-year project by the UK's innovation agency, Innovate UK to deliver a molecular breast imaging device. The radiation monitoring company said the project, commencing in mid-2018, is worth ?1.4mln.
Echo Energy Plc (LON:ECHO) has told investors that the second well workover in Argentina has been a success. The CSo-80 well, within the Fracci??n D asset, was opened up in a previously untapped reservoir section and a combination of oil and water flowed to surface, the company revealed.
Hurricane Energy PLC (LON:HUR) has appointed Steven McTiernan as the company's new non-executive chairman, effective May 1. He will replace interim chair David Jenkins who will return to his position as senior independent director.
Highlands Natural Resources Plc (LON:HNR) said after market close on 20 April that it now has funding for six additional wells at its East Denver Niobrara shale oil and gas project in Colorado.
Savannah Resources Plc (LON:SAV) is pushing ahead with pre-feasibility work at the Mutamba mineral sands project in Mozambique. Four license applications are under consideration by the Mozambican mines department and Savannah will shortly take a 10 tonne bulk sample.
Tlou Energy Ltd (LON:TLOU) updated investors on its activities in the three months ended March 31, in which the company focussed on the Lesedi and Mamba coal bed methane (CBM) projects in Botswana. At Mamba, the company successfully drilled its first core-hole, and it purchased a drilling rig to facilitate a programme of multiple additional core-holes.
Diversified Gas & Oil plc (LON:DGOC) said it has expanded its workforce and strengthened senior management following its acquisitions of Alliance Petroleum Corp (APC) and oil and gas assets from CNX Gas Company (CNX).
Ferrum Crescent Ltd (LON:FCR) has appointed Spanish consultancy Mining Sense to advise and assist in exploration work and preparation for a preliminary economic assessment at the Toral lead-zinc project in Spain.
The FTSE 100 is set to make a subdued, but positive start to the trading week, ignoring both the negative end to proceedings on Wall Street and mixed trading in Asia Monday.
According to the spread betting firms the index of blue-chip shares will open 15 points to the good at 7383.17, building on the 39 point gain on Friday.
But after a four-week recovery period there are concerns the momentum is starting fade.
Michael Hewson, analyst at CMC Markets, reckons some markets in Europe are starting to look "a little tired", though he cited the DAX and the Euro Stoxx 50 ahead of the UK benchmark.
However, one wonders whether the rebound in UK-listed commodity stocks, buoyed by higher oil and metal prices along with the drop in the pound, will continue.
Looking at the scheduled corporate news, Shire (LON:SHP) will find out on Wednesday whether rival Takeda is serious with its enhanced ?43bn bid for the UK-listed Irish druggie. For this is the deadline for a formal bid.
Meanwhile, the banks and pharma companies get UK earnings season into full swing with reports from Royal Bank of Scotland (LON:RBS), Lloyds (LON:LLOY), Barclays (LON:BARC) and GlaxoSmithKline (LON:GSK).