Deloitte undertook too much non-audit work for Autonomy to be 'sufficiently independent' from the software firm that Hewlett Packard bought last year and which it now accuses of inflating its accounts.

That's the view of PIRC, the shareholder group, which advises companies collectively worth £1.5trn on corporate governance.

HP, which paid $11.1bn (£7bn) for the firm last year - criticised as too much by some analysts at the time - and announced this week that it was writing off around $5bn (£3.1bn) due to 'serious accounting improprieties' which it claims inflated the numbers prior to the deal.

The British firm has denied any wrongdoing, but its accounts are now mired in a contentious storm of attrition between its founder, Mike Lynch, and HP.

'Prior to its takeover, Autonomy raised a number of red flags on the governance front,' PIRC told Reuters.

'In PIRC's view it lacked proper independent representation, which led us to oppose the election of numerous directors over years. Its auditor also raked in significant non-audit fees, which we found problematic.'

PIRC said the amount Autonomy paid the Big Four firms for additional services such as legislation, tax and corporate finance advice came to more than 25% of the total the group paid Deloitte, a level PIRC believes is significant in its assessment of whether an auditor is 'properly independent from its client'.Autonomy paid Deloitte $2.7m in 2010, with $1.5m described as total audit fees and the rest described as non-audit fees.

Alan MacDougall, PIRC's managing director, told Reuters that shelling out for unrelated fees to auditors undermined their independence, although it was common practice, with around 40 FTSE 350 business engaged in such practices.

Reuters said Deloitte had told them that their audit work was fully compliant with all regulations and professional standards and 'categorically denied' any misrepresentations in Autonomy's financial statements.

The firm said neither HP nor Autonomy had contracted it to provide any acquisition-related due diligence, while HP says it relied on Deloitte - an ICAEW member - for the vetting of Autonomy's vital statistics.

The ICAEW's website clearly states that its ethical guidance in the UK imposes no limits on the types of income an auditor can generate from a client.

However, it says independence is maintained by stipulating 'that income from any one client, for whatever service, is kept to no more than a certain proportion of that firm's overall practice income'.