Linklaters is advising G4S over a potential Serious Fraud Office (SFO) investigation into claims that the company has been overcharging for electronically tagging criminals in England and Wales.

Justice secretary Chris Grayling told the House of Commons yesterday (11 July) he wanted the SFO to investigate the private security firm, which he says has been "[charging] in ways not justified by the contracts and for people who were not in fact being monitored".

Linklaters partners Richard Godden and Tom Lidstrom have been advising G4S for the last few months, with Grayling in May announcing he had ordered an independent audit of G4S' and rival Serco's bills by accountants PriceWaterhouseCoopers (PwC).

In his statement, Grayling told MPs that G4S and Serco have been overcharging the government by tens of millions since both contracts commenced in 2005, and had charged Government for people who had never been tagged, who had left the country, returned to prison or died.

Grayling said Serco has agreed to co-operate with a subsequent forensic investigation by PwC, and has also withdrawn from the current tender process to renew the tagging contracts.

However, he added that had G4S had rejected a proposal to undertake a further detailed forensic audit, and that he would ask the SFO to investigate the matter further.

Grayling said: "Given the nature of the findings of the audit work that has taken place so far, and the very clear legal advice that I have received, I am asking the Serious Fraud Office to consider whether an investigation is appropriate into what happened in G4S, and to confirm to me whether any of the actions of anyone in that company represent more than a contractual breach."

"I am disappointed that G4S still feel it appropriate to participate in the tendering process for the next generation of electronic monitoring contracts, which we are currently in the process of renewing. I have therefore started a formal process to determine whether to exclude them from this competition."

In a statement, G4S said: "G4S has co-operated fully with the PwC audit and is committed to co-operating with all audits of current contracts to the full extent provided under those contracts."

G4S added that it is conducting its own review, assisted by external advisers, and "is not aware of any indications of dishonesty or misconduct".

Grayling said he had also launched a disciplinary investigation into the way the contracts had been managed inside the Ministry of Justice after uncovering evidence that officials knew in 2008 there were problems with how both companies were billing for tagging.