Withers faces a £1.6m damages bill after losing a professional negligence claim related to the drafting of an LLP agreement.

However, the High Court also rejected three other claims of negligence brought by the firm's former client, executive search company Wellesley Partners (WP).

Withers acted for the headhunters in 2008 over the admission of a number of new partners to its LLP. These included Addax Bank – a Bahraini bank – which was to invest about £2.5m to acquire a 25% interest in the partnership.

This required the drafting of a new LLP agreement which was completed on 14 May 2008 giving Addax the option to withdraw half its capital contribution at any time within the first 41 months. However, WP said its instructions to Withers were that the option should only be exercisable after 42 months, which was reflected in an earlier draft. Addax exercised the option after 12 months.

In its defence, Withers claimed that it made the change on the instructions of WP's principal owner, Rupert Channing. Though the lawyer involved had no recollection or record of the conversation during which the firm said the instructions were given, he insisted he would not have changed the draft otherwise.

The judge, Mr Justice Nugee, found that there must have been some discussion of the clause, but said Channing did not intend Withers to make the change, nor indeed did he understand that it had done so.

He ruled that the solicitor "must have either misunderstood the instruction, or noted it down wrong, or when he came to redraft [the clause] misremembered what he had been instructed".

Nugee J went on to dismiss three other claims of negligence. The damages mainly represented the loss of profit from not undertaking expansion that WP would have undergone had Addax not withdrawn its money.

In a statement Withers said: "We respect the judgment of Mr Justice Nugee. We are pleased that he dismissed three of the four claims against us and, in relation to the fourth claim, acknowledged the uncertainty as to what instructions our client had given us. The amount of damages awarded is one fifth of the amount claimed, and we believe our former client could have avoided incurring large costs had he accepted our settlement offer."