Addleshaw Goddard is set to lose another senior litigator to a disputes spin-off practice as tensions rise between the national firm and the departing partners.

Michael Green is set to join colleagues Simon Twigden and Pietro Marino, who are setting up their own litigation boutique specifically targeting claimants, along with three associates.

Green (pictured), who made partner in 2005, has acted for clients including Equitas, Capita Insurance Services, Matrix-Securities and LF Insurance.

Marino and Twigden – two of the firm's top litigators – both handed in their notice in April and are currently serving out their 12-month notice period, although negotiations are taking place to arrange an earlier departure from the firm. A number of associates are likely to follow Twigden and Marino, but exact figures are currently unclear.

However, it is understood that tensions have risen between Addleshaws and the exiting partners over issues such as clients, which include Russian oligarch Boris Berezovsky, and how ongoing matters will be handled after the team's departure. Marino successfully advised Berezovsky in his multibillion-pound claim against Roman Abramovich, which in March was given permission to proceed to trial next year.

Twigden was the top 20 law firm's national practice head but was replaced as litigation chief by the firm's insurance and reinsurance practice head Richard Leedham after handing in his notice.

Addleshaws denied there was an issue with the departing partners and maintained that their relationship with the firm is cordial. A spokesperson for Addleshaws said: "We are not prepared to comment on clients and who they instruct."

The departing partners declined to comment.