Martineau Johnson, which has existed as a single office firm in Birmingham since 1828, is to break with tradition and open in the City.
The new core office, opening on 4 September, will be headed by Edge Ellison partner Heather Leeson, a specialist in banking litigation and recovery work.
She will be bringing with her Chris Wright, an associate also from Edge Ellison, and all but one of their support team.
One source at Martineaus says that it is hoped she will bring a large proportion of clients too.
Martineaus' move is in response to suggestions from an increasing client base of London companies, particularly Lloyds TSB, with which the firm has a relationship dating back to the 1800s, when the bank became incorporated.
Martineaus' managing partner David Gwyther says: "In recent years we've heard our clients saying that there would be more work if we were to practice in London."
Previously the firm has only had a non-contentious banking and finance practice, but the new additions, with extensive experience of banking litigation, will create a new facet in this area.
Gwyther says: "We will be able to provide an extension to the services we've been offering to Lloyds and our other clients."
Gwyther says Leeson and Wright had been unsettled since moving to Edge Ellison from ill-fated Stones Parker. Their decision to leave came before talk of the merger with Hammond Suddards.
An official statement issued by Martineau Johnson claims that the new development does not represent any plans for major expansion in the City.
A spokesperson says: "We have no ambition to be a magic circle firm. We are just looking at the opportunities in London and growth will be appropriate to the market."