Investors have taken legal action against HP over its bodged acquisition of Autonomy, which shareholders claim has resulted in the company’s falling stock price.

The suit follows HP’s announcement of a £5.5 billion writedown of Autonomy, after an internal investigation allegedly found that the British company was substantially overvalued at the time of acquisition. It said that Autonomy had misrepresented its financial performance, including its revenue, core growth rate and gross margins, and misrepresentation of its business mix.

Autonomy founder and CEO Mike Lynch completely denied the claims and instantly reverted the blame back to HP and the auditors that were involved with the acquisition.

Both the US Securities and Exchange Commission and the UK’s Serious Fraud Office have been alerted to the claims.

According to the Financial Times, the class action suit that has now been filed against HP claims that it issued false and misleading statements on its financial performance and prospects between August 2011, when the Autonomy deal was announced, and 20th November this year, when it announced the multi-billion pound writedown.

Robbins Geller Rudman & Dowd, a firm specialising in class action lawsuits, filed against HP on Monday in San Francisco, and named only one investor that has been affected, Allan Nicolow.

He bought 200 shares in May at $21.87 (£13.64) each. HP shares closed at $11.71 (£7.30) on 20th November.

The suit names Leo Apotheker, former CEO of HP, Meg Whitman, current CEO, Cathie Lesjak, chief financial officer, and Jim Murrin, former chief accounting officer.

It claims that when HP had agreed to acquire Autonomy ‘in principle’, the defendants (Apotheker etc.) were looking to unwind the deal “in light of the accounting irregularities that plagued Auonomy’s financial statements.”

The suit also claims that the defendents had concealed from investors the extent of the decline of HP’s Enterprise Services Business, which is made up largely of its $14 billion (£8.7 billion) acquisition of EDS.

Research group IDC has said that HP customers should seek ‘formal assurances’ about the future of Autonomy’s products.