The Serious Fraud Office has charged two former employees of the outsourcing firm Serco with fraud and false accounting, as its investigation into contracts awarded by the government for the electronic tagging of prisoners continues.

Serco said it was “mortified” earlier this year after it paid a £23m fine to the SFO as part of the investigation, which included allegations of charging for tagging people who were either dead, in jail, or had left the country.

The SFO said on Monday it had brought charges against Nicholas Woods, the former finance director of Serco Home Affairs, and Simon Marshall, former operations director of field services.

Both were charged in relation to representations made to the Ministry of Justice between 2011 and 2013. Woods was also charged with false accounting in relation to the 2011 statutory accounts of Serco Geografix.

As part of the settlement agreement Serco reached with the SFO earlier this year, it reports annually to the SFO and the Cabinet Office on a programme to ensure it upholds ethical standards.

Concerns about the prisoner tagging contract were first reported by Serco to the SFO in 2013.

Solicitor Andrew Katzen, of Hickman and Rose, who is representing Woods, said: “Mr Woods is very disappointed that the SFO has decided to charge him with criminal offences dating back to his work at Serco about 10 years ago. The SFO has spent six years investigating this matter and Mr Woods fully cooperated throughout.

“He denies the allegations and looks forward to the opportunity of clearing his name.”