France-based Ardian has agreed to acquire British insurer’s Jardine Lloyd Thompson (JLT) Group’s 26.2% stake in Milestone, the holding firm of Siaci St Honoré, JLT's French associate.

Terms of the deal were not disclosed.

JLT Group chief executive Dominic Burke said: "Ardian is one of the pre-eminent private equity investors in the European market and are well placed to take the business forward. "

With net proceeds of £82.1m being payable in cash and used to repay borrowings, the proposed deal will create an approximate gain of £21m for JLT, in 2015.

Milestone gross assets were around £457m, as of 31 December 2013, while profit before tax for the 12 months to the same year was £24m, and its contribution as an associate to JLT was £5m.

Subject to the signing of a definitive sale agreement by all parties and the approval of antitrust authorities, the deal is expected to be completed by the end of April this year.

Siaci St Honoré offers insurance broking and employee benefits services in France, while Ardian is an independent private investment firm with assets of $50bn managed or advised in Europe, North America and Asia.

Siaci St Honoré and JLT will continue to work in multiple joint ventures and initiatives in areas including energy, construction, marine & cargo and credit & political Risk, as well as service shared international clients on a global basis.