(Reuters) -Precision instruments maker Spectris agreed on Monday to a 4.4 billion pound ($5.9 billion) debt-inclusive takeover deal by private equity firm Advent over a rival proposal from KKR, marking the biggest acquisition in Britain this year.

Britain has in recent years drawn overseas buyers due to its relatively cheap valuations, and this latest deal could be another blow to a London stock market which has been weakened by takeovers, shifts in listing venues and sluggish IPO activity.

Spectris shares jumped almost 15% to 37.68 pounds in early trade to their highest in over a year, and were the biggest percentage gainer on London's mid-cap FTSE-250 index.

Last week, the British company, which provides hardware and software solutions to the pharmaceuticals, steel and automotive sectors, rejected a second takeover bid from KKR in favor of Advent's offer, but did not reveal any terms of KKR's proposal.

KKR said on Monday that it was still engaging with the Spectris board and although no revised offer has been made, it was in advanced stages of due diligence and securing financing commitments, without giving details of its proposal.

Under Advent's offer, each Spectris shareholder will receive 37.63 pounds per share in cash, the companies said, which also includes an interim dividend of 28 pence.

Advent also said that each Spectris shareholder will receive the final dividend for fiscal year 2024 with no reduction to its cash offer per share.

Spectris said it intends to unanimously recommend the Advent deal to its shareholders.

"The Board remains confident in Spectris' strategy ... but believes that Advent's offer recognises the attractiveness of Spectris and represents strong and immediate cash value for shareholders at an attractive premium," Spectris Chairman Mark Williamson said in a statement.

Advent's offer is at a premium of 84.6% to Spectris' closing price on June 6, the day before any acquisition interest was disclosed.  

($1 = 0.7443 pounds)

(Reporting by Raechel Thankam Job and Yamini Kalia in Bengaluru; Editing by Sonia Cheema, Mrigank Dhaniwala and Emelia Sithole-Matarise)