Defunct German firm Haarmann Hemmelrath is set to appeal against a Duesseldorf court ruling ordering the firm to pay a chunk of the legal costs following its successful defence of a negligence claim from a former client.

The court ruled that costs, which are understood to be in the region of €20m (£14m), should be split between the two parties, but the law firm says former client Werhahn should foot the whole bill.

The infamous €400m (£275m) negligence claim, brought by Werhahn in 2004, is thought to have been the largest ever claim against a European law firm. Werhahn said Haarmanns had been negligent when advising it on the sale of one of its subsidiaries, a claim that was later ruled as "groundless" by the German courts.

As well as the dispute over the costs of the original case, Haarmanns, which went into liquidation last December, has since announced intentions to counter-sue the German holding company for damages, blaming the negligence suit for the firm's demise.

Court proceedings regarding the damages claim are yet to begin, but could be influenced by the outcome of the ruling on costs.

Former managing partner Wilhelm Haarmann told Legal Week: "The ruling is not to our satisfaction, so we will appeal against it and take it to the next instance."

He added: "Although the rulings are connected, we are still confident we will be able to go ahead with the claim for damages."

At its peak, the German giant had 660 lawyers, tax advisers and accountants, but the firm came to an acrimonious end amid management discord and rows over profit sharing.