CALLS have been made for the Scottish Government to audit its £13 million electronic tagging contract with G4S after the Serious Fraud Office was called in to investigate the security firm.

The firm, along with Serco, overcharged the UK Government by tens of millions of pounds, including costs for monitoring dead offenders.

It comes a year after G4S was criticised for failing to recruit enough staff to protect the Olympics.

The Scottish Government has awarded G4S a five-year contract for electronic tagging of offenders.

Alison McInnes MSP, the Scottish Liberal Democrats' justice spokeswoman, said: "We need to know whether the Scottish Government will act to protect the taxpayer and conduct a full audit of the company's tagging operation."

Coalition Government Justice Secretary Chris Grayling admitted contract managers in the Ministry of Justice discovered issues as far back as 2008 but did nothing.

A Government-wide review of all contracts held by Serco and G4S was also sparked.

Mr Grayling is planning to privatise up to 70% of the Probation Service, but unions called on the Justice Secretary to block the firms from the tendering process

The likes of G4S and Serco were set to bid for a wide range of contracts to supervise low to medium-level offenders across England and Wales.

Ian Lawrence, general secretary of the National Association of Probation Officers (Napo) union, said: "These companies are unfit for purpose when it comes to holding important public contracts."

An audit by PwC revealed overcharging began at least as far back as the start of the current contracts in 2005, but could have dated back to 1999.

Auditors discovered the firms had charged the Government for tagging offenders who were back in prison, had their tags removed, had left the country or had never been tagged in the first place.

Mr Grayling has told the firms an independent forensic audit must be conducted to look at, among other areas, email trails between executives. While Serco has agreed to take part, G4S has refused.

The Justice Secretary said: "The billing practices in question were unacceptable and the Government will take all necessary steps to secure a refund for the taxpayer."

Serco has agreed to withdraw from the current tender process for electronic monitoring, while the Justice Secretary is to instigate moves to exclude G4S as the company is attempting to bid.

Serco had been the leading bidder for upcoming prison contracts in Yorkshire, but Mr Grayling will delay this contract.

An urgent review of contract management across the Ministry of Justice's major contracts has also been launched.

A Scottish Government spokesman said the contract was entirely separate.

He added: "Should any practices arise that give cause for concern then the appropriate action would be taken under contractual remedies or, if required, by reporting the circumstances to law enforcement agencies." It said it routinely audits the electronic monitoring service provider to ensure the service, as it is set out in the electronic monitoring contract, is being delivered.