West Bromwich Building Society is converting its sales team into mortgage brokers to sell from its own newly created panel of lenders.
The society is also believed to be looking to buy an IFA operation.
The broker service will be available through West Brom's branch network.
It will aim to advise borrowers outside its mortgage range or those failing its lending criteria on a variety of more suitable loans from lenders on its panel.
Seven lenders have so far signed up, including Nationwide, NatWest, Woolwich, Royal Bank of Scotland and sub-prime lenders Kensington and Platform Home Loans.
The society believes the scope of mainstream and adverse-credit products from its panel of lenders cover “99 per cent” of borrowers' requirements.
West Brom says it will assess the composition of the panel of lenders on a quarterly basis.
Other non-panel lenders are understood to have been called in to act as consultants to help in its transition to mortgage broker.
Existing West Brom advisers are undergoing training on the range the panel of lenders offer and will be supported by a product helpline at the society's central office once the service is running.
A spokesman says: “We are involved in a lenders' panel, which is to offer borrowers mortgages that we are unable to offer ourselves or are more suitable for those who do not meet our lending requirements.”