Serco's chairman Alastair Lyons has fallen on his sword and announced that he will step down from the embattled outsourcing company after the group repeatedly downgraded its profits and confirmed it would have to launch a rights issue.

"Since the events of last year I have sought to stabilise Serco with strong new management and non-executive directors; a much improved relationship with the UK Government; and clarity as to our strategic direction," said Lyons, who became chairman in May 2010.

"The initial findings of the strategy and balance sheet review point to strategic and operational mis-steps at Serco for which, as chairman of the board since 2010, I take ultimate responsibility. It is also the right thing for Serco to select a new chairman, to take the helm for the future.

"Whilst colleagues have asked me not to resign, it has been my intention to step down once a new strategy and direction for the business were in place. I am, therefore, taking the necessary steps to ensure an orderly process for my own succession during the first half of 2015."

On 10 November, Serco shares plunged by nearly 35% in the market open after the security firm revealed that it would have to launch a rights issue. The firm said it wanted to raise £550m (€701m, $875m), to take the sting off the £1.5bn in impairment charges it was hit with.

A rights issue in a publicly traded company is an offering of shares to existing shareholders, rather than to the general public, to raise a cash quickly without going to a bank for a loan.

"Whilst I respect Lyon's decision, I want to put on record the fact that he has done an outstanding job stewarding the company through the travails of the last twelve months," said Rupert Soames, CEO at Serco.

"Nobody could have worked harder or done more to get us to the point where we can now concentrate on building a solid future for Serco."