Slump in Weir leads UK's FTSE down from record high

* FTSE 100 down 0.5 pct after Tuesday's record high

* Weir Group falls sharply after revenue warning

* Whitbread (LSE: WTB.L - news) gains on encouraging outlook (Adds details)

By Atul Prakash and Alistair Smout

LONDON, Feb 25 (Reuters) - Britain's top share index retreated from the previous session's record high on Wednesday, with engineer Weir Group leading the market lower after warning about a significant drop in its revenue in the current year.

Weir Group, which makes valves and pumps for the energy and mining industries, fell nearly 9 percent to the bottom of the blue-chip FTSE 100 index after saying uncertainty in the oil and gas industry would significantly reduce its revenue despite cost-cutting.

"People have been talking about inevitable cutbacks in oil exploration for quite along time, and you would have thought that those companies with exposure to the sector would have already been on investor radar screens," Jeremy Batstone-Carr, market analyst at Charles Stanley (LSE: CAY.L - news) , said.

"Given that, it's surprising that there's been such a sharp reaction to Weir's outlook statement."

The blue-chip FTSE 100 index was down 33.59 points, or 0.5 percent at 6,916.04 points by 1509 GMT after setting a new record high of 6,958.89 points on Tuesday. That surpassed its previous high of 6,950.60 set on Dec (Shanghai: 600875.SS - news) . 30, 1999.

Among other sharp movers, mid-cap AO World slumped nearly 30 percent after the British online domestic appliances retailer cut its full-year earnings outlook as the hype around the company's flotation faded.

On the positive side, Whitbread rose 2.4 percent after saying it expected to post full-year profit toward the top end of market forecasts, as strong demand at its Premier Inn hotels and Costa Coffee chain helped deliver a 5.8 percent rise in fourth-quarter underlying sales.

"Despite tough comparatives, Whitbread continues to defy economic gravity driven largely by the ongoing growth at Premier Inns and Costa in particular," Richard Hunter, head of equities at Hargreaves Lansdown Stockbrokers, said.

"Even so, investors will have few complaints on a growth stock where the share price has risen 22 percent over the last year. Despite this rapid appreciation, the market remains committed to the story with the consensus still coming in as a comfortable buy."

St James's Place was also in demand, with its shares rising 4.4 percent to the top of the FTSE 100's gainers list after it posted forecast-beating full-year cash profits, boosted by a rise in assets that underpinned a surprise increase in the firm's final dividend. (Editing by Tom Heneghan)