Accenture, the consultancy, has described as “baseless and without merit” a £182m claim from British Gas over the disastrous introduction of its new billing system.

Centrica, owner of British Gas, was forced to write off almost £200m as a result of problems with the system, which came into use in 2006.

Customer complaints against British Gas soared, and it was forced to hire up to 2,500 additional staff at one point to deal with the problems created.

It also had to pay for extra work and commit management time to fixing the system. It is now claiming those costs back from Accenture in a writ filed at the High Court last week.

Centrica is expected to talk about the case at its annual general meeting on Monday.

Accenture was hired in 2001 to design and implement the new system, known as Jupiter.

As British Gas switched to the new system in 2006, complaints about mistakes in billing mounted, reaching a peak in the second half of that year and into early 2007.

Having been seen earlier in the decade as one of the better energy suppliers for customer service, it became seen as by far the worst, although complaints have subsequently fallen sharply.

British Gas alleged in a statement : “Accenture was responsible for fundamental errors in the design and implementation of the system.” It said this assessment had been delivered by another consultancy hired to analyse the problem.

However, Accenture said it rejected responsibility.

It said: “Centrica directed the design, build and implementation of the Jupiter system and insisted on many of the features they now find problematic.”