WOS.L Share News (WOS)

* 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 indexedged lower in light trade on Tuesday, with most stocks fallingin thin volumes ahead of the European Central Bank's meetingthis week, while substantial buying of shares in plumbingsupplier Wolseley provided some support.

Wolseley rose 2.1 percent, to be the top FTSE 100gainer, after it reported a 5.1 percent rise in third-quarterlike-for-like revenue and said it expected sales to grow about 4percent in the next six months.

"With around 70 percent of its profits generated in theU.S., the company provides a good way of playing the ongoingrecovery in housing and construction markets," Killik & Codirector of market research Paul Kavanagh said.

Trading in Wolseley shares was twice its 90-day average by1410 GMT, and was one of only 13 FTSE 100 stocks in positiveterritory.

The majority of stocks fell in trading volume of just athird of the index's 90-day average.

The blue-chip FTSE 100 index was down 0.5 percent at6,829.75 points by 1412 GMT, not far from a 14-year high of6,894.88 on May 15. The index is 1.7 percent below its recordhigh of 6,950.60 set in late 1999.

Traders said that investors were reluctant to make strongbets one way or the other ahead of a meeting of the ECB onThursday. Expectations of policy action have helped to pinshares near highs. Tuesday's unexpected euro zone priceinflation fall in May, increasing the risks of deflation, piledon the pressure for the ECB to act at its meeting on Thursday.

"He's almost promised too much, so he'll have to deliversomething. If he doesn't, the market will tank, and if it does,it's probably priced in," ETX Capital's head of trading, JoeRundle, 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 along-term refinancing operation targeted at businesses.

Among individual losers, G4S dropped 1.6 percentafter the Financial Times reported the global security companywas under further pressure as a British government-fundedwatchdog agreed to investigate its activities in Israel and thePalestinian territories. (Additional reporting by Atul Prakash; Editing by LouiseIreland)