Linklaters and PricewaterhouseCoopers (PwC) have so far netted £2m in fees from client G4S for an ongoing independent review into allegations its employees engaged in false billing practices between 2005 and 2013.

The fees have been accrued in less than six months, with G4S only opening the review in June. The private security company has asked Linklaters to assess whether there was evidence of dishonesty or criminal conduct by employees who billed the Ministry of Justice (MoJ) as part of an electronic monitoring contract.

The FTSE 100 company said Linklaters' review has so far identified no evidence of dishonesty or criminal conduct by any G4S employee.

The magic circle firm is also advising G4S in relation to a Serious Fraud Office (SFO) probe on the same matter.

Linklaters' team has been led by commercial litigation partner Tom Lidstrom and corporate partner Richard Godden, who also advised G4S on issues arising from problems with its Olympic contract last summer.

"The review has confirmed that, in certain circumstances, G4S Care & Justice Services wrongly considered itself to be contractually entitled to bill for monitoring services when equipment had not been fitted or after it had been removed," G4S said on Tuesday (19 November).

In total, the company incorrectly billed the MoJ for £23.3m between 2005 and May 2013 and a further £0.8m since June 2013. G4S apologised and offerd £24.1m in credit notes to the MoJ, which has not yet been accepted.

Earlier this month, the SFO confirmed it had opened its own investigation into the matter, following calls from Justice Secretary Chris Grayling.

The MoJ is also conducting an audit in relation to the billings and the company's assessment of the matters. G4S said it would work with the MoJ to resolve any outstanding matters.

G4S group chief executive Ashley Almanza said Linklaters' review represented "months of intensive work by an independent law firm and external accountants".

"[It] is an important step in setting this matter straight and restoring the trust which has been earned by our many thousands of committed and hard-working employees over many years."