Olswang is facing a multimillion-pound claim relating to advice it gave on the £460m acquisition of fitness club chain Esporta from private equity firm Duke Street Capital announced in 2006.

The case, which has been assigned to the Queen's Bench Division of the Commercial Court, sees Olswang accused of negligence and breach of its duties of care under its client retainer in relation to advice it gave Esporta's acquirers Ironzar III, a trust owned by property investor Simon Halabi.

Ironzar claims Olswang breached its retainer duty by failing to alert the trust of the potential pitfalls created by the format of letters of engagement between the trust and Ernst & Young (E&Y), which was conducting due diligence on the acquisition. It also alleges Olswang failed to provide E&Y with the necessary documents it required as part of its due diligence exercise.

Ironzar has also issued a claim against E&Y, alleging it overpaid for the Esporta chain on the back of inflated membership numbers and income in E&Y's reports.

The claim against Olswang is for damages of £25m in relation to breach of duty of care, and/or £138.3m and/or £72.2m relating to the alleged failure to provide E&Y with the correct documentation, plus interest.

A spokesperson for Olswang confirmed: "Proceedings were issued just before the expiry of the limitation period without any prior notification or complaint to Olswang.

"The main focus of the claimant['s] allegations about the failed transaction is advice relating to the Esporta acquisition given by another professional. The complaints against Olswang are peripheral to the main allegations and are highly speculative. We have reviewed the complaints made and are satisfied that we acted appropriately. The proceedings are ongoing."

Ironzar has turned to dispute resolution boutique Grosvenor Law and 4 New Square's Roger Stewart QC and Richard O'Brien. Clyde & Co professional and financial disputes partner Sarah Clover is acting for Olswang. Grosvenor declined to comment.