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* FTSE 100, mid caps flat
* Miners weigh; WPP slides after H1 results
* Oil, financials, weak pound supportive
By Kit Rees
LONDON, Sept 4 (Reuters) - The UK's top shares index came under pressure on Tuesday as a drop among mining stocks and WPP shares weighed, though a weaker pound and boost from big oil kept losses limited.
The blue chip FTSE 100 .FTSE index was flat in percentage terms at 7,503.90 points by 0856 GMT, as were mid caps .FTMC .
A drop among mining stocks as copper prices declined was the biggest weight on the FTSE, while a fall in WPP's WPP.L shares dragged on consumer discretionary stocks.
WPP dropped as much as 8.5 percent after the advertising company cut its profit margin guidance as the group restructures, though it did raise its net sales outlook. results were slightly better at the top-line, and slightly worse at the margin level than expected," analysts at Liberum said in a note.
WPP's shares were set for their biggest one-day fall in around five months.
Despite WPP's decline, a rise across financials, large consumer staple stocks and big oil stemmed losses on the index. A weaker pound was also a help.
"The significantly weaker pound boosted the FTSE in the previous session, lifting it notably above its peers on mainland Europe. However, the UK index has been unable to hold on to that momentum," analysts at London Capital Group said.
Shares in DS Smith SMDS.L were up more than percent after the packaging group said in a trading update that it sold more boxes at higher prices in the first quarter. in engineering firm Smiths Group SMIN.L also gained 1.6 percent on the back of a media report that it rebuffed ICU's ICUI.O latest offer for its medical unit. updates were also in focus among mid cap stocks. Shares in Halfords Group HFD.L were the biggest gainers, up 6.5 percent after the automotive and cyclical products retailer reported a rise in underlying sales in a tough trading environment. also maintained its full year profit outlook.
Some analysts were a little hesitant to be so upbeat after the update, however.
"While the year has started well with a robust trading update, the shares are likely to remain in limbo until Graham Stapleton gives his first strategic update on 27th September and a clear view on the investment needed to return the business to profit growth," analysts at Investec said in a note, referring to Halford's new chief executive.
Halford's shares are flat on the year.