The increasingly bitter battle between Hewlett-Packard (HP) and Autonomy has entered a new phase as the UK's Serious Fraud Office (SFO) is set to investigate the £7.5bn deal.

The SFO has become the third body, alongside the Financial Reporting Council, the UK's accounting watchdog, and the US Department of Justice, to investigate HP's claims that it was forced to massively overpay for the software giant in August 2011.

In November 2012, HP wrote down £5.4bn on the £6.7bn price tag over its claims that Autonomy had misled them about its financial health. Autonomy has denied this.

An SFO spokesperson confirmed that allegations had been made to the SFO about the circumstances of the sale in 2011 of Autonomy to Hewlett Packard. 'The director of the Serious Fraud Office has decided to open an investigation into those allegations, with a view to using its powers of investigation to allow them to be tested. It is, of course, right to point out that the opening of a criminal investigation does not mean that individuals are guilty of a crime or indeed that a crime has been committed.

'It has also been reported that the SFO uses an Autonomy product, Introspect, as a document management tool. The SFO is keen to ensure that there is now no conflict of interest or perception of such a conflict, and it is obliged as a first step to make inquiries to ensure that it can continue as the investigating body. It is undertaking this work at present,' the spokesperson said.

The SFO said it will make no further comment while its investigation is underway.

Last month the FRC launched its investigation under the Accountancy Scheme into the published financial reporting of Autonomy for the period between 1 January 2009 and 30 June 2011.

The FRC's decision to initiate an investigation was taken following consultation with the ICAEW and came after the US Department of Justice's probe which began late last year.

The latest investigation comes as HP prepares for its AGM, scheduled to take place in California later this week.