Centrica ended 9.8 percent lower, its biggest one-day percentage drop since late 2008 and wiping off more than 1 billion pounds from its market capitalisation, after saying it would sell shares to pay off debt.

Inmarsat, which provides communications for shipping and aircraft, fell 7.2 percent after the company cut its revenue guidance, citing a tough trading environment and weakening demand.

The blue-chip FTSE 100 index <.FTSE> closed 0.09 percent higher at 6,117.25 points, a day after hitting a one-month low.

Investors were confronted by a survey of activity in Britain's dominant services industry, which showed the British economy slowed in April and may stall as consumers worry about June's referendum on whether to remain a member of the European Union.

"There has been some speculation that these poor numbers, if sustained, could prompt speculation about the need for further stimulus, or a rate cut," said Michael Hewson, chief market analyst at CMC Markets.

"However, this seems premature at a time when inflation is showing some signs of picking up and wage growth still remains above the level of inflation."

Losses in companies like Centrica and Inmarset were offset by advances elsewhere. BT rose 2.6 percent to lead the gains after its results beat expectations.

BT said it would spend 6 billion pounds ($8.7 billion) to roll out super-fast fibre and 4G mobile in the next three years, following demands by regulators for improved service.

RSA rose nearly 2 percent. The insurer's operating profits for the quarter also beat expectations, though net written premiums dipped.

Morrisons was up 2.4 percent after it reported quarterly sales improved further The supermarket had dropped 1.7 percent on Wednesday after poorly received figures from rival Sainsbury and weak Kantar data.

"The group's 'back-to-basics' approach (is) finding favour with shoppers. The price war, though, goes on and the threat from discounters remains," said Russ Mould, investment director at AJ Bell.

ADVISORY- Reuters plans to replace intra-day European and UK stock market reports with a Live Markets blog on Eikon (see cpurl://apps.cp./cms/?pageId=livemarkets for site in development). In a real-time, multimedia format from 0600 London time through  the 1630 closing bell, it will include the best of our market reporting, Stocks Buzz service, Eikon graphics, Reuters pictures, eye-catching research and market zeitgeist. Breaking news and dramatic market moves will continue to be alerted to all clients and we will continue to provide a short opening story and comprehensive closing reports.

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    Mike Dolan, Markets Editor EMEA.

($1 = 0.6903 pounds)

(Additional reporting by Atul Prakash; Editing by John Stonestreet)

By Alistair Smout