By Sara Sjolin

COPENHAGEN (MarketWatch) -- ARM Holdings PLC posted the biggest gain in London on Monday after its customer Apple Inc. confirmed a tie-up with China Mobile, while banks also helped lift the benchmark index.

The FTSE 100 index rallied 1.1% to close at 6,678.61, rising for a fourth-straight day.

Shares of ARM Holdings PLC (ARMHY) put on 3.9% after Apple Inc. (AAPL) confirmed on Sunday that it has at long last reached a deal with China Mobile to officially carry the iPhone. Apple uses ARM technology in its iPhones, and Marc Kimsey, senior trader at Accendo Markets, said the U.K. chip designer is poised to benefit from the deal as well.

"[China Mobile] boasts more than 750 million subscribers; put into context, the entire U.S. population consists of 'just' 318 million. With ARM technology in every Apple handset, the potential is obvious. Expect to see Apple's 5% share of the $80 billion Chinese smartphone market increase significantly in 2014," he said in a note.

Banks were also higher in London. Shares of Standard Chartered PLC rose 2.4%, Barclays PLC (BCS) gained 1.8%, HSBC Holdings PLC (HSBC) put on 1.4% and Royal Bank of Scotland Group PLC (RBS) added 0.8%.

Shares of Serco Group PLC gained 2.8% outside the main index after the government-services firm said it secured a six-month extension to its contract with the Australian Government Department of Immigration and Border Protection to provide detention services at centers on mainland Australia and Christmas Island.

Shares of British Sky Broadcasting Group PLC gained 2.3% after Fitch Ratings affirmed the long-term rating on the cable TV-provider at BBB+ with a stable outlook.

On a more downbeat note, shares of Premier Foods PLC slid 3.8% after the U.K. food producer said it is still reviewing its capital structure and that it includes the possibility of a rights issue.

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