Bond Dickinson is to formally tie up with its US alliance partner, Womble Carlyle Sandridge & Rice, combining as Womble Bond Dickinson.

The two firms struck an alliance in June 2016 but have now taken this relationship a step further, although stopping short of financial integration.

The union will go live in October under a company limited by guarantee structure, with the combined firm housing more than 420 partners and 1,000 lawyers across eight UK offices and 15 US offices.

With combined revenue of more than $410m (£340m), it will sit within the UK top 20, based on last year's results, and within the AmLaw 100.

According to the Legal Week UK top 50 2015-16, Bond Dickinson is the 39th largest law firm in the UK, with revenue of £104m ($134m) and an average profit per equity partner of £275,000.

Data from the American Lawyer 200 2017 shows Womble posting revenue of $281m (£219m) in 2016,  making it the 114th largest law firm in the US.

Both firms will be equal members of the new company, with both continuing to operate separate and autonomous partnerships with their own independent management.

Four members from each firm will sit on the board of the new entity, which will be co-chaired by managing partner of Bond Dickinson, Jonathan Blair, and Womble Carlyle chair and CEO, Betty Temple.

Womble Carlyle is particularly strong in the southeastern and mid-Atlantic states, with five of its 15 offices in North Carolina.

Bond Dickinson was formed through the 2013 merger between Bristol-headquartered Bond Pearce and Newcastle-based Dickinson Dees.

The company limited by guarantee structure has been used in a number of recent transatlantic tie-ups, including those between UK firm Eversheds and US firm Sutherland Asbill & Brennan and Canadian firm Gowlings and UK firm Wragge Lawrence Graham & Co.

Temple said: "This exciting combination elevates our offering and proposition in the US, to ensure we are consistently in tune with the evolving ambitions and needs of all our clients and that we can successfully execute on our growth strategy."

Blair said: "The agreement creating Womble Bond Dickinson marks the achievement and culmination of our vision to be a top 20 law firm by 2020. This combined firm enables us to provide an enviable transatlantic platform for further expansion and growth in the UK, where London remains a priority for investment, along with Edinburgh and other regional areas important to US and UK clients."

The UK firm has offices in Aberdeen, Bristol, Leeds, London, Newcastle, Plymouth and Southampton.

Womble Carlyle has five offices in North Carolina, three offices in South Carolina and two offices in Virginia. It also has offices in Palo Alto; Wilmington, Delaware; Washington DC; Atlanta, Georgia; and Baltimore.

In 2014, Bond Dickinson signed an alliance with German firm Redeker Sellner Dahs. The firm also has a bilateral relationship with a firm in France but has no international offices.