Next month’s £710m court battle over the biggest legal acquisition in history is set to last until Christmas, one of the parties confirmed today.

Slater and Gordon is pursuing Watchstone Group (formerly known as Quindell) for £637m – the value at which it bought the company’s professional services division in 2015. Watchstone is countersuing for £63m.

In its half-year report, Watchstone confirmed that the High Court hearing, set to start on 21 October, is now expected to last for nine weeks.

The plc has provided an extra £2.7m to cover its legal costs as the scope of work required to be undertaken has broadened and the trial approaches. This has included the review of almost 600,000 documents and other files, leaving Watchstone with ‘no option’ but to pay the costs of disclosure from some third parties.

The £3.9m provision set aside last December to cover legal costs has now been spent, the company confirmed.

Slater and Gordon has issued proceedings for alleged breach of warranty and/or fraudulent misrepresentation in advance of the Quindell acquisition, a purchase which was followed by a collapse in the firm’s parent company’s share price and massive financial losses.

Watchstone has denied any misrepresentation ‘in the strongest terms’ and has vowed to defend the claims robustly. Earlier this month, the company obtained permission from the High Court to file an amended defence and counterclaim in the proceedings. The counterclaim results from allegations about the disclosure process pre-acquisition and Watchstone insists the professional services division may actually have been under-valued as a result. Slater and Gordon has not commented on this allegation.

Aside from the legal actions, Watchstone confirmed the Serious Fraud Office investigation continues – more than four years after the SFO said it was probing the business and accounting practices at Quindell.

There have been no further developments on the threatened class action litigation first announced in September 2015.