Watson Farley & Williams has defeated a £10m professional negligence claim for a second time after an appeal against the firm was thrown out by the Court of Appeal last month.

International businessman Itzhak Ostrovizky sued Watson Farley after investments he made in Greek solar energy projects before the financial crisis failed, incurring loses of around €13m (£9.5m), according to Ostrovizky.

Watson Farley partner Virginia Murray had been retained to draft three purchase agreements for Ostrovizky.

The firm commenced proceedings to claim some £25,000 in unpaid fees back from Ostrovizky in 2011; however, he counterclaimed that Murray had been negligent in drafting the agreements.

That counterclaim was rejected last year. Ostrovizky went on to appeal the decision, but his appeal was rejected by Lady Justice Arden, Lord Justice Pitchford and Lord Justice Burnett last month.

"Had the process been as quick as the parties hoped in the early stages, all would probably have been well," Justice Arden said in her judgment. "But as it dragged out over years, good money was thrown after bad, the financial climate changed and the deals unravelled. In my judgment, the judge's conclusion that none of that could be attributed to Ms Murray's drafting or actions in 2007 cannot be faulted."

Watson Farley managing partner Chris Lowe said: "Our position has always been that these claims were without merit and we are pleased the Court of Appeal has upheld the ruling of the High Court, which dismissed all claims against Watson Farley & Williams."

Irwin Mitchell acted for Watson Farley, instructing QCs Michael Pooles of Hailsham Chambers and Gary Blaker of Selborne Chambers.

Clyde & Co led for Ostrovizky, instructing 4 New Square's Ben Hubble QC.