Osborne Clarke is to resign from the Legal Resources Group the network of four regional firms which share a Brussels office.
The remaining three firms in the group Dickinson Dees, Pinsent Curtis and McGrigor Donald will take their training in-house but continue to share the Brussels office and to hold regular meetings.
The restructuring is scheduled for 1 May next year, when Osbornes formally resigns, but joint legal training courses are already being run down.
Leslie Perrin, Osbornes' managing partner, said the firm established its own Brussels office six months ago by linking with Belgian firm Huysmann & Partners, and felt it could tailor training to the firm's needs better by doing it in-house.
Huysmann has joined Osbornes' existing European alliance, which has offices in Paris, Copenhagen, Frankfurt, Barcelona and Rotterdam. Osbornes has no permanent staff at the Huysmann Brussels office but its lawyers use the office as required.
"Since we've already got an office in Brussels, we don't particularly need the LRG one as well," said Perrin. But he stressed: "It's not a falling out we've had a fantastic run with LRG for 10 years. It's more a case of growing pains."
Dickinson Dees managing partner, Graham Wright, who is currently chairman of LRG said that following Osbornes' resignation, all three other members had felt that training could be better done in-house particularly McGrigor Donald, which worked in a different jurisdiction. The joint training programme will be run down and cease at the end of April.
But Wright said the Brussels office and the regular detailed information sharing meetings would continue among the remaining firms after 1 May, and that informal relations with Osbornes would also continue.
The LRG was founded 10 years ago and is regarded as one of the most successful of the regional law firm alliances. Its training courses are highly-regarded, and its "benchmarking" sessions where detailed performance and profitability figures are compared have been a useful tool for the firms' respective managing partners.
But its member firms have changed strategy over the years. Two regional LRG members Simpson Curtis and Pinsent & Co merged to form a firm with national ambitions in 1995. Osbornes has expanded in London and no longer sees itself as a regional practice.
Liverpool firm Alsop Wilkinson was asked to leave the alliance when it merged with national firm Dibb Lupton Broomhead, a Pinsent Curtis competitor, last year.