(ADVISORY- Follow European and UK stock markets in real time on the Reuters Live Markets blog on Eikon, see cpurl://apps.cp./cms/?pageId=livemarkets)
* FTSE 100 closes up 1 pct at 6,919.42 points
* Shell, BP rise after OPEC agrees supply curbs
* But Capita slumps after profit warning
* FTSE 100 up roughly 10 pct since start of 2016
By Alistair Smout and Adela Suliman
LONDON, Sept 29 (Reuters) - Britain's top share index approached a 1-1/2 year high on Thursday, boosted by heavyweight oil companies after a decision by OPEC to curb output for the first time since 2008.
Outsourcing group Capita, however, missed out on the broader market rally, slumping 26.7 percent after issuing a profit warning.
The blue-chip FTSE 100 index closed up 1 percent at 6,919.42 points, within touching distance of its 2016 peak of 6,955 points which was its highest level since April 2015.
A rise in the shares of oil companies was the main driver behind the FTSE's gains, with Royal Dutch Shell jumping more than 6 percent while BP climbed 4.3 percent following the OPEC decision.
Although details on the OPEC deal were scarce, traders were encouraged by the group's first move to support prices since 2008.
"This tentative move by OPEC could be a game changer and as a result we're seeing oil stocks moving up quite nicely," said Manoj Ladwa, head of trading at TJM Partners.
The FTSE 100 is up roughly 10 percent since the start of 2016.
A decision by the Bank of England in August to cut interest rates to record lows helped the FTSE 100 recover from an initial slump in June caused by Britain's shock 'Brexit' vote to quit the European Union. (Additional reporting by Kit Rees; Editing by Angus MacSwan and Susan Fenton)