A west London district general hospital has snubbed a merger bid from Imperial College Healthcare Trust, opting instead to join with an established foundation trust, HSJ understands.

HSJ has learned the board of West Middlesex University Hospital Trust has chosen Chelsea and Westminster Hospital Foundation Trust as its preferred merger partner, rejecting a competing bid from Imperial.

The £149m-turnover West Middlesex conceded last year that it could not become a foundation trust on its own, and would instead seek a merger.

After an early expression of interest from Hillingdon Hospitals Foundation Trust was rejected, the contenders were narrowed down to Imperial and Chelsea and Westminster.

A senior source involved in the process said the West Middlesex board’s decision came down to a choice between better-aligned patient referral flows with Imperial or an absence of performance issues with Chelsea and Westminster.

The decision was taken at a private meeting of the board on 26 February.

The £343m-turnover Chelsea and Westminster Hospital Foundation Trust is considered one of London’s most efficient trusts; £950m-turnover Imperial has seen improvements but is still considered to have performance problems in several areas.

Former Chelsea and Westminster chief executive Heather Lawrence was last year appointed to run NHS London’s acute efficiency programme.

A merger between West Middlesex and Chelsea and Westminster would create an organisation with a turnover well above £400m a year. One senior figure in the policy world told HSJ that hospital trusts would need an annual income in excess of that figure to survive the cost pressures and reductions in funding coming over the next two financial years.

The decision of West Middlesex’s board will now have to be ratified by the NHS Trust Development Authority, which had not responded to requests for comment as HSJ went to press.

HSJ understands the plan for services at West Middlesex would be similar whichever bidder was selected.

Commissioners designated the trust as one of the five major hospitals in north west London earlier this month.

This means a full accident and emergency service will be retained on its private finance initiative-funded site. HSJ understands the plan is to move more elective orthopaedic work to West Middlesex.

The trust owes a significant legacy debt to the Department of Health, following bailouts in 2006, which any merger partner would be likely to want written off.