The fledgling lender has offered its products through John Charcol brokers since last summer as part of a pilot scheme between the bank and the firm.
Metro Bank has since engaged in discussions with other firms and networks and an enlargement of its broker channel is now imminent.
Mortgage Solutions understands that expansion will take place this month.
The bank currently lends only on properties located in London and the South East of England.
Metro Bank launched in July 2010 and currently operates from 16 branches in London and the South East. It has long-standing plans to grow its chain to 200 branches by the end of the decade.