* FTSE 100 index up 0.1 pct
* GSK's profit warning erases FTSE gains
* Strong figures from Capita, BHP Billiton keep index afloat
By Francesco Canepa
LONDON, July 23 (Reuters) - A profit warning by heavyweight drugs firm GlaxoSmithKline took the shine of Britain's top equity index on Wednesday, offsetting gains in outsourcing group Capita and miner BHP Billiton.
Shares in GSK fell 5 percent, their worst drop since 2008, after the firm cut its 2014 earnings outlook, casting a shadow on its future payouts to shareholders.
"The share price has come off sharply on the back of weak quarterly results and forward earnings guidance which is very uninspiring," said Ketan Patel, of Ecclesiastical Investment Management, which is a shareholder in GSK.
"There will be concerns over the level of the payout ratio ... and low or no growth in the dividend."
The stock knocked 14 points off the FTSE 100, which was up 3.75 points, or 0.1 percent, to 6,799.09 points by 1422 GMT. It had traded as high as 6,822.65 points before GSK's update was published at 1100 GMT.
Johnson Matthey fell 1.2 percent after the world's biggest producer of automotive catalytic converters posted an 11-percent fall in first-quarter underlying profit and said it expected a worse-than-expected impact from a stronger British sterling.
Bank of England officials discussed this month whether there was a case for an early rate rise, but were held back in part by strikingly low wage growth and signs of weakness abroad, minutes showed on Wednesday.
Helping support the FTSE, Capita rose 4 percent to the top of the FTSE 100 after the group, which runs services from the Ministry of Defence pension scheme to police radio systems, posted an 11 percent rise in first-half organic revenue.
While Capita has benefited from scandals over the private provision of public services which damaged rivals G4S and Serco, the group's strong results also reflect central and local government and private sector companies outsourcing work to cut costs in the face of tighter budgets.
"Some of Capita's peers have struggled with reputational challenges with the UK government so the business has been a partial beneficiary from that," David Brockton, an analyst at Liberum, said.
"More specifically, Capita's improved growth is also ... a function of recovering levels of spend in some of the areas that suffered through the downturn."
Volume on the stock was already twice its full-day average for the past three months, compared with volume of half the average for the FTSE 100 as a whole.
Mining shares added 4 points to the index after BHP Billiton beat its own guidance for full-year iron ore output and seeing productivity gains across a number of businesses.
Some investors, however, were steering clear of large direction bets on the index due to political concerns, with the EU raising the prospect of restricting Russian access to European capital markets, defence and energy technology, and due to the conflict in Gaza. (Additional reporting by Atul Prakash; Editing by Alison Williams)