The UK's Serious Fraud Office said it had closed its investigation into the ill-fated sale of IT firm Autonomy to Hewlett-Packard in 2011.

The Serious Fraud Office said there was insufficient evidence for a realistic prospect of conviction. 

The US company had referred the $11.1 billion deal to the British authorities after it announced an $8.8 billion writedown in November 2012, with more than $5 billion put down to accounting fraud. 

The British company and its executives have denied anywrong doing.

HP, which bought Autonomy to lead a shift into software, alleged "some former members of Autonomy's management team used accounting improprieties, misrepresentations and disclosure failures" to inflate the company's apparent worth. 

Autonomy's former chief executive Mike Lynch, a mathematics whiz who led the firm when it was sold, has blamed the fall in its valuation on HP's mismanagement.

Fallout from the purchase included the departure of two Hewlett-Packard directors, and prompted Chairman Ray Lane to give up that post. It also included criminal and civil probes by authorities in the US and UK.

HP, based in California, said it passed information from an unidentified whistleblower to the US Department of Justice, the SEC and the SFO. 

"In respect of some aspects of the allegations, the SFO has concluded that, on the information available to it, there is insufficient evidence for a realistic prospect of conviction," the British authority said today. 

It said it had ceded jurisdiction over the case to US authorities, whose investigation is ongoing. 

Last year, HP reached a deal over litigation with shareholders over the botched acquisition, that involved shareholder lawyers agreeing to drop all claims against HP's current and former executives, including chief executive Meg Whitman. 

In return, HP said it would pursue claims against former Autonomy executives, including Lynch. A federal judge later rejected the proposed settlement.