Britain's FTSE posts third straight month of gains

* FTSE 100 down 0.5 pct

* Banks, Berkeley Group lead the gainers

* Miners track metals prices lower

* Restaurant Group falls on downgrade (ADVISORY- Follow European and UK stock markets in real time onthe Reuters Live Markets blog on Eikon, see cpurl://apps.cp./cms/?pageId=livemarkets)

By Kit Rees

LONDON, Aug 31 (Reuters) - UK shares ended lower onWednesday, hit by a late slump in the energy sector, althoughthe FTSE 100 posted its third monthly gain in a row.

The blue chip FTSE 100 index closed down 39.28 points, or0.6 percent, at 6,781.51 points, slightly underperforming thebroader European market. The index ended the month up 0.8percent, and has risen 6 of the last 7 months.

The FTSE 100 is now 7 percent above its pre-Brexit level,helped by a fall in sterling. The FTSE 250 has alsorecovered, up 2.3 percent since Britain's June 23 vote to leavethe European Union.

"The market seems to be relatively buoyant and that's notreally surprising given that interest rates are so low. There'snot many other options in terms of where money is going to flowother than the stock market, given the historic low yields onbonds and cash not really producing very much," said LaithKhalaf, senior analyst at Hargreaves Lansdown.

But commodity-related stocks came under pressure Wednesday.

Energy stocks were the biggest weight on the FTSE 100,trimming 15.8 points off the index. The sector extended fallsafter U.S. data revealed a large build in crude supplies.

Mining companies also slid as metals prices dropped.Randgold Resources, Fresnillo, BHP Billiton, Anglo American and Rio Tinto droppedbetween 2.1 and 5 percent.

However, banking stocks Barclays HSBC Holdings and Lloyds Banking Group all rose 0.8 percentto 1.8 percent after a series of encouraging reports on theBritish economy, with the boss of Deutsche Bank also calling formore M&A within the sector.

The latest showed British consumer morale in Augustrecovered somewhat from the slump that followed the Brexit vote.Another, from mortgage lender Nationwide, said house price risespicked up speed more than expected in August .

The house price data buoyed housebuilder Berkeley Group, which was the top gainer with a 3 percent rise,despite worries that it could be relegated from the FTSE 100 inan upcoming reshuffle.

Outside the blue chips, Restaurant Group dropped 5.9percent after Citigroup cut its rating on the stock to "sell".

"Restaurant Group's share price has bounced over 50 percentof late. Given this significant move, and the view that thegroup faces ongoing operational headwinds, we once againdowngrade the stock recommendation to Sell," Christopher JMcVey, an analyst at Citigroup, said in a note.

(Editing by Mark Heinrich)