* FTSE 100 index falls 0.5 percent
* Wolseley rises after update
* Caution before ECB's policy meeting
* G4S hit by new scandal (Adds quote, fresh prices)
By Alistair Smout
EDINBURGH, June 3 (Reuters) - Britain's top share index edged lower in light trade on Tuesday, with most stocks falling in thin volumes ahead of the European Central Bank's meeting this week, while substantial buying of shares in plumbing supplier Wolseley provided some support.
Wolseley rose 2.1 percent, to be the top FTSE 100 gainer, after it reported a 5.1 percent rise in third-quarter like-for-like revenue and said it expected sales to grow about 4 percent in the next six months.
"With around 70 percent of its profits generated in the U.S., the company provides a good way of playing the ongoing recovery in housing and construction markets," Killik & Co director of market research Paul Kavanagh said.
Trading in Wolseley shares was twice its 90-day average by 1410 GMT, and was one of only 13 FTSE 100 stocks in positive territory.
The majority of stocks fell in trading volume of just a third of the index's 90-day average.
The blue-chip FTSE 100 index was down 0.5 percent at 6,829.75 points by 1412 GMT, not far from a 14-year high of 6,894.88 on May 15. The index is 1.7 percent below its record high of 6,950.60 set in late 1999.
Traders said that investors were reluctant to make strong bets one way or the other ahead of a meeting of the ECB on Thursday. Expectations of policy action have helped to pin shares near highs. Tuesday's unexpected euro zone price inflation fall in May, increasing the risks of deflation, piled on the pressure for the ECB to act at its meeting on Thursday.
"He's almost promised too much, so he'll have to deliver something. If he doesn't, the market will tank, and if it does, it's probably priced in," ETX Capital's head of trading, Joe Rundle, said, referring to ECB head Mario Draghi.
The ECB is widely expected to trim its refinancing rate, send its deposit rate into negative territory and launch a long-term refinancing operation targeted at businesses.
Among individual losers, G4S dropped 1.6 percent after the Financial Times reported the global security company was under further pressure as a British government-funded watchdog agreed to investigate its activities in Israel and the Palestinian territories. (Additional reporting by Atul Prakash; Editing by Louise Ireland)