G4S faces continued pressure over the Olympics security debacle, as share prices continued to fall.

On Tuesday bosses at the private security firm insisted they would be claiming tens of millions of pounds in management fees despite admitting being 100% responsible for a "humiliating shambles".

By the end of Tuesday, G4S shares had fallen 17% since the crisis emerged last Wednesday, wiping £700 million from its market value.

And in a further twist on Tuesday night, retired police officers claimed they were told that they were no longer needed to help with security at the Olympics because they were "surplus to requirements".

Chief executive Nick Buckles is under pressure to quit his £830,000-a-year job over the fiasco, which has resulted in the emergency deployment of soldiers, marines, airmen and police officers.

Mr Buckles admitted on Tuesday he was sorry and "deeply disappointed" after the firm failed to deliver on its £284 million contract, saying he could not deny the debacle was a "humiliating shambles for the company". But he repeatedly insisted the firm still intended to claim its £57 million management fee for work over the last two years.

Keith Vaz, chairman of the Commons Home Affairs Select Committee, said it was "astonishing" and called on G4S to waive the fee and any others associated with the contract, while other MPs on the committee also criticised the firm.

Mr Buckles promised G4S would pay all police and military costs caused by its failure, cover any accommodation expenses and consider paying bonuses to individual officers and troops if considered appropriate. But asked why the firm still wanted to claim its management fee, he said: "We've managed the contract and we've had management on the ground for two years. We still expect to deliver a significant number of staff."

Meanwhile, on Tuesday retired police officers claimed they were told they were no longer needed to help with security at the Olympics because they were "surplus to requirements". David Anderton, secretary of the Merseyside branch of the National Association of Retired Police Officers, said just days after he was sent an email offering employment at the Games for retired officers, he was sent another from the private security firm saying further recruitment was "surplus to requirements" because of the deployment of military and extra police resources.

G4S said the letter was sent about a week ago at a time when it had been refused dispensation to use former police officers who had not completed necessary training and accreditation, and they were not "surplus to requirements" but lacked necessary accreditation and cannot be employed at London 2012.