Top-ten building society the West Bromwich has boosted its business further by taking over a leading mortgage intermediary.

It has acquired Derby-based Mortgage Force, a franchise operation, for an undisclosed sum, it was announced late yesterday .

The deal by the West Brom, which last year grew its asset base by 17 per cent to £5 billion, is thought to be one of the first of its kind in the building society sector.

Mortgage Force provides support and services to a nationwide network of 100 independent mortgage advisers and is based on an Australian model imported into Britain by chief executive Robert Clifford.

Each of its advisers is regulated by the Financial Services Authority.

The benefit for the West Brom, which already has chalked up some 200,000 customers outside of its core trading area in the West Midlands, is that its home loans will now get a far wider exposure, even though Mortgage Force's advisers are not tied exclusively to its products.

Roger Smith, group development officer at the West Brom, said last night: "The ability to meet customers' needs and reach new markets through UK-wide specialist one-to-one advice is reflected in the rapid growth of this pioneering operation."

Mr Clifford said that Mortgage Force's status as a private company was proving to be a constraint on a "fiercely-ambitious" business.

"To achieve further rapid growth we need to be part of a much larger operation."

The West Brom is expected to build on a five-year track record of growth under chief executive Andrew Messenger by growing assets to about £6 billion in the current year.