Commodity stocks help Britain's FTSE outperform Europe

* FTSE 100 up 1.5 pct

* Miners benefit from Credit Suisse (LSE: 0QP5.L - news) upgrade

* Oil sector rises on hope for output deal

* Mid cap Mitie posts record fall on profit warning (ADVISORY- Follow European and UK stock markets in real time on the Reuters Live Markets blog on Eikon, see cpurl://apps.cp./cms/?pageId=livemarkets)

By Alistair Smout and Adela Suliman

LONDON, Sept 19 (Reuters) - British shares gained on Monday, outstripping European peers thanks to a rise in commodity-related stocks, though mid cap Mitie Group (Other OTC: MITFF - news) slumped nearly 30 percent after a profit warning.

The blue chip FTSE 100 index closed at 6,813.55, up 103.27 points or 1.5 percent, posting its biggest daily rise in two weeks. Energy and basic materials firms combined to add 30 points to the index.

Mining companies Anglo American (LSE: AAL.L - news) , BHP Billiton (NYSE: BBL - news) , Glencore (Xetra: A1JAGV - news) , and Rio Tinto (LSE: RIO.L - news) were all at the top of the board, up between 3.5 to 6.2 percent, benefiting from upgrades by Credit Suisse.

Glencore was the top gainer on the index after it was raised to "outperform", and the bank lifted its target price for the other three. In all, miners were up 4.3 percent

Oil and gas shares rose 1.7 percent after crude prices advanced. Venezuela said a deal to stabilise oil markets could be announced this month, shrugging off U.S. data that showed the market was well supplied with oil.

Some were sceptical over the prospects for a deal, however.

"I struggle to get too carried away until we get a confirmed deal. There's been too many false dawns with regards to output agreements," said Craig Erlam, senior market analyst at broker OANDA.

"These comments from Venezuela suggest something may be in the offing but until something concrete happens we can't buy into it too much."

The FTSE 100 bounced back after posting its second straight week of losses on Friday, weighed down by a sell-off in banks after U.S. authorities demanded Germany's Deutsche Bank (LSE: 0H7D.L - news) pay $14 billion to settle a mortgages case.

Analysts said they expected markets to be volatile ahead of Wednesday's interest rate decisions from the Bank of Japan and U.S. Federal Reserve.

"I don't necessarily think (the rise) is an indication of really strong sentiment - I think markets are more likely to be a bit up and down before the (central bank) meetings," Jasper Lawler, market analyst at CMC Markets (LSE: CMCX.L - news) , said.

While only a handful of FTSE 100 stocks suffered losses, mid cap Mitie Group plunged 28.9 percent on the FTSE 250 , its biggest daily loss ever, after issuing a profit warning.

The outsourcing firm lowered its full-year operating profit outlook, citing a reduction in higher-margin project volumes and spending by clients in the wake of Britain's vote to leave the European Union. (Additional reporting by Kit Rees; Editing by Mark Trevelyan)