(For a live blog on European stocks, type LIVE/ in an Eikon news window)
* FTSE 100 up 0.2 pct
* A number of shares trading ex-dividend
* CRH rises after H1 report
By Julien Ponthus
LONDON, Aug 23 (Reuters) - UK shares were slightly up on Thursday with energy stocks lifting the blue-chip FTSE 100 .FTSE following a rally in crude oil, while ongoing trade war tensions between China and the United States kept investors on their toes.
The British index was up 0.24 percent at 7,952.5 points at 0901 GMT with shares in the energy sector contributing to roughly half of the gains.
Heavyweights Royal Dutch Shell RDSa.L and BP BP.L were up 0.9 percent and 0.8 percent respectively.
Smaller firms in the sector such as Tullow Oil TLW.L and Premier Oil PMO.L , which announced profits for the first half of the year, were also rising. Both were up 3.2 percent.
"From a fundamental point of view, while growing fears for a trade war was a main story in the last few weeks, investors are now betting on crude again, due to the sharp drop in U.S. oil supply and the escalation of tension with Iran", said Carrlo Alberto De Casa, chief analyst at ActivTrades.
CRH CRH.L was up 0.7 percent after the building material firm published a trading update.
"Weather disruption has not prevented building materials business CRH from chalking up a solid first half", said AJ Bell investment director Russ Mould.
Shares in gambling software maker Playtech PTEC.L were the best performing among mid-sized companies, gaining 9.4 percent after first-half results showed double-digit growth in many of its developed markets.
A number of stocks, notably in the financial sector, such as Prudential PRU.L , Royal Bank of Scotland RBS.L or the London Stock Exchange LSE.L were trading without entitlement to their latest dividend pay-out trimming 4.24 points off the FTSE 100.
Miners and basic materials groups were also weighing on the broader index, with copper prices falling while the trade dispute between Washington and Beijing continued to trigger concerns about demand for industrial metals.
Fresnillo FRES.L , Anglo-American AAL.L lost both 1.1 percent.
"The fact the FTSE avoided a sharp drop after the bell is something of a surprise given the woeful state of the commodity sector this Thursday", commented Spreadex analyst Connor Campbell.