Adds background from source in paragraphs 7 and 8

By Raechel Thankam Job

July 21 (Reuters) - British outsourcer OCS Group International will buy listed rival Mitie MTO.L for £3.1 billion ($4.17 billion), the companies said on Tuesday, forming a facilities management firm positioned to tap booming demand for AI-driven infrastructure services.

OCS will pay 218.5 pence per Mitie share in cash, plus a dividend of 3.1 pence per share. The total offer of 221.6 pence per share represents a 46.8% premium to Mitie's closing share price on Monday.

Mitie's shares shot up over 40% in early trading to a record high of 214 pence, but still below the offer price.

Panmure Liberum analyst Joe Brent said the deal is likely to succeed, with a small possibility of a rival bid, reflecting the sector's appeal to buyers.

"There is clearly a scale advantage, and data is becoming increasingly important," he said.

OCS, owned by U.S. private investment firm Clayton, Dubilier & Rice, operates across the UK, Europe, the Asia-Pacific region, and the Middle East, serving the business services, healthcare, technology, and financial services sectors.

Talks began earlier this year, before June, and took a few months to finalise, a source familiar with the matter told Reuters, adding that the discussions were partly accelerated by the planned retirement of Mitie CEO Phil Bentley.

CD&R could list the combined business in the UK when it decides to exit it, said the source who spoke on condition of anonymity to discuss the private talks.

Under Bentley, Mitie has delivered a turnaround across its businesses since 2023. It counts Microsoft MSFT.O and Google GOOGL.O among its clients and provides mechanical, electrical, cooling and security systems for hyperscalers.

Bentley, who had planned to retire by March 2027, will remain with the company until completion of the transaction, which is expected in the first quarter of 2027, the companies said.

Separately, Mitie reported a 10% rise in revenue for the quarter ended June 30, supported by new contract wins, including data centre projects and engineering services at AstraZeneca's AZN.L global research hub.

Mitie has suspended its £100 million share buyback programme in light of the proposed acquisition by OCS.

The deal is the latest in a string of takeovers that have shrunk London's stock market, as buyers target what many analysts view as undervalued UK companies.

($1 = £0.7439)