Commodities lift FTSE 0.4 pct to 15 mth high

* FTSE 100 posts fifth straight session of gains

* Index recovers to pre-Lehman levels, up 22 pct this year

* Commodity stocks stronger; banks retreat

LONDON, Dec 29 (Reuters) - Britain’s top share index gained for a fifth straight session on Tuesday, hitting a 15-month peak on its return from the festive break, boosted by strength in mining stocks, though gains were tempered by weaker banks.

By 0917 GMT the FTSE 100 .FTSE was up 0.5 percent or 26.22 points at 5,48.63, recovering to levels not seen since before the collapse of Lehman Brothers in September 2008.

The blue chip index added 0.6 percent on its last previous trading session on Dec. 24, with gains that week at almost 4 percent.

Miners added most the points to the index as as metal prices marched higher. Rio Tinto RIO.L, Xstrata XTA.L, Lonmin LMI.L, Anglo American AAL.L, Kazakhmys KAZ.L and BHP Billiton BLT.L gained between 1 and 2.2 percent.

“The Santa rally hasn’t petered out yet and I think we’ll be on a forward trajectory until we get into January and start to re-evaluate things,” said Howard Wheeldon, strategist at BGC Partners.

The blue chip index has gained almost 57 percent since hitting a six-year trough in March and is up 22 percent for the year, on track for its biggest yearly gain since 1997.

The last 10 years have seen the lowest rate of economic growth in Britain in the post-war period, and the worst set of returns for investors on the stock market since the Great Depression, a Financial Times analysis of official market data has revealed.

The analysis, drawn from data supplied by the Office for National Statistics, showed that in real terms GDP rose on average by 1.7 percent annually over the decade, which represents the worst economic expansion since the 1940s.

Banks were the biggest weight on the index, retreating from sharp gains made before the holiday period.

Barclays BARC.L, HSBC HSBA.L and Standard Chartered STAN.L lost 0.2 to 0.9 percent. But Royal Bank of Scotland RBS.L and Lloyds Banking Group LLOY.L -- both part-nationalised -- were both in slightly positive territory.

Retailers were slightly weaker despite early signs that there was a strong Christmas trading period.

Bellwether British retailer John Lewis [JLP.UL] reported a strong online start to its seasonal clearance sale, adding to signs shoppers might be out in force ahead of a rise in VAT on Jan. 1. It also reported a strong online start to its seasonal clearance sale. [ID:nLDE5BR0B2]

Marks & Spencer MKS.L, Next NXT.L and Home Retail HOME.L, however, fell 0.1 to 0.4 percent.

Among individual fallers, British Airways BAY.L retreated 0.9 percent dented by concerns that increased airport security as a result of an attempted terrorist attack on a U.S. Northwest Airlines flight over the Christmas period would add to the airlines woes.

In the absence of much corporate or economic data coming out of the UK, investors will watch for the U.S. Case Shiller house price survey due for release at 1400 GMT and U.S. consumer confidence data released at 1500 GMT. (Reporting by Simon Falush; Editing by Hans Peters)