Bircham Dyson Bell (BDB) and Pitmans have agreed to merge following a partner vote, and will also convert the combined firm into an alternative business structure (ABS).

The new firm, which will have combined revenues of more than £50m, will be called BDB Pitmans and officially launch on 1 December.

The two firms announced that they were in advanced merger talks earlier this month.

Legacy BDB managing partner Andrew Smith and chief operating officer Mark Jones will lead the combined firm with Helen Ratcliffe, legacy BDB's senior partner, taking up the same post at BDB Pitmans.

Meanwhile, legacy managing partner of Thames Valley legal outfit Pitmans John Hutchinson will sit on the executive board, alongside legacy Pitmans deputy managing partner Suzanne Brooker and legacy Pitmans senior partner David Archer.

BDB Pitmans will have offices in London, Cambridge, Reading and Southampton and a combined workforce of 80 partners and more than 400 staff.

Smith said: "We are delighted that the partnership voted overwhelmingly in favour of this merger. From our earliest discussions we saw clear alignment, both in the cultural fit between the two firms and the practical benefits of what our combined offering geographically and in practice areas would bring to our clients and our people."

The new ABS structure of the firm will, once it has received regulatory approval, allow it to bring non-lawyers into the equity and share profits. Big Four accountancy firms have been making a significant push into this area in recent months.

Key clients of BDB include Transport for London, National Grid and London Luton Airport Limited, while Pitmans clients include SKY, ferry company Red Funnel, UK investment bank and stockbroker finnCap and housing developers Vanderbilt Homes.