Law firm Arthur Cox has had to replace half the partners in its Belfast office after a spate of defections in April and June.

The firm maintains the departures are not a setback, even though the departees included two of the three partners in its lucrative corporate finance practice. The solicitors in question were Peter Stafford and Mark Thompson, who left in April with commercial partner Patricia Johnston. They established Stafford Thompson Johnston to compete with established Belfast firms.

Another partner - Anne Beggan - left Arthur Cox in June to join the Belfast firm Tughans.None of the departures have been reported in the Dublin media.

Arthur Cox has had to appoint four new partners to bring its Belfast office back to full strength.

One of the top firms in Dublin, Arthur Cox is the only company with a practice on both sides of the Border. Other Dublin firms have alliances with Belfast firms.

When asked about the impact of the departures on the firm's business, a spokesman said "this is not a setback".

He said the departees in April declared their intention to leave as early as January and said the firm had retained all its major clients. "These changes happened more than six months ago and the Belfast office has since developed to its strongest level yet, through organic growth, new hires and the successful management of the partners' departure.

"The firm currently has eight partners and will make further announcements in the coming months." Mr Stafford said he and his colleagues had "no particular rancour" with Arthur Cox, but felt there were business opportunities to be exploited.

Their new firm has already had a role in several big-ticket transactions, he said.

"We just felt there was a gap in the market that could be exploited by three ambitious, well-connected lawyers. We were thinking about it for about six months before we pushed the button on it and it wasn't a particularly difficult thing to do."