Marks & Spencer share rally boosts blue-chip FTSE index

* Benchmark FTSE 100 index rises 0.7 percent

* M&S shares gain 7.9 percent after results

* Meggitt (Other OTC: MEGGF - news) up 6.5 percent on share buyback plan

By Atul Prakash

LONDON, Nov 5 (Reuters) - Britain's top share index advanced on Wednesday, with retailer Marks & Spencer (Other OTC: MAKSF - news) leading the market higher after raising its margin outlook and aircraft parts supplier Meggitt gaining on its plan to start a share buyback programme.

Meggitt shares rose 6.5 percent, even as the company cut its expectations for 2015 in the latest downgrade in a series, blaming delays in the U.S. military market and financial difficulties being faced by its partner in Brazil.

Marks & Spencer rose 7.9 percent, the biggest gainer in the blue-chip FTSE 100 index, after Britain's top clothing retailer by revenue posted a rise in underlying first-half profit for the first time in four years and raised its guidance for non-food gross margin for 2014-15.

"Gross margin has shown a strong improvement, in part due to the tight control of costs which M&S is currently undertaking, whilst the roll out of more 'Simply Food' stores over the next three years aims to capitalise on the way the market is developing," Richard Hunter, head of equities at Hargreaves Lansdown Stockbrokers, said.

"In addition, the group is confident that it is set for the impending Christmas period, whilst the extra cash generation has enabled a modest raising of the dividend."

The UK General Retailers Index rose 1.5 percent, the biggest sectoral gainer, and helped the benchmark FTSE 100 index to rise 0.7 percent to 6,496.18 points by 0856 GMT after falling 0.5 percent in the previous session.

However, resource-related stocks lost ground. The UK mining index fell 0.4 percent, tracking a drop of 0.8 to 1.5 percent in key base metals prices, after data showing growth in China's services sector weakened further in October. China is the world's biggest metals consumer.

Precious metals miners were also hit by a slump in gold and silver prices to four-year lows, with Randgold Resources falling 2.6 percent, the biggest decliner in the FTSE 100 index. (Reporting by Atul Prakash; Editing by Toby Chopra)