Two ambulance crew have been sacked by G4S after leaving a voicemail message for a vulnerable patient in which they suggested they could “beat the fuck” out of him with a fire extinguisher and then claim self-defence.

Last month the Guardian revealed that the driver of the two-man non-emergency G4S ambulance crew told his colleague that “beating a patient to a pulp” was preferable to “being beaten to a pulp”, even if they were prosecuted.

His colleague suggested that to do so would simply result in a six-month suspension while they were investigated. The two-man crew were immediately suspended when it was brought to G4S’s attention.

The driver of the G4S vehicle initially left a message saying the crew would be a few minutes late to take him to William Harvey hospital in Ashford, Kent. But he failed to complete the call correctly, and the crew’s conversation was recorded on the voicemail.

“He’s homeless, he’s aggressive, he’s suicidal, so he ain’t gonna be the best, is he?” the driver was heard to say. “You don’t need to take him if you don’t feel safe with him. That’s why we’ve got the fire extinguisher. Take it off the hook now and you’ve got something to hit him with. You’d rather be prosecuted, wouldn’t you, for beating a patient to a pulp than that patient beating you to a pulp, wouldn’t you, as a choice of the two?”

The driver continued: “D’you want a broken arm, a broken jaw, black eyes, or do you want to beat the fuck out of someone and then get prosecuted? You could still say it was self-defence.” His colleague added: “And get suspended for six months while they check up on it.”

The driver concluded: “[At] least you’re able to sit in your garden. You wouldn’t be able to get into your garden with a broken leg, would you?”

The 43-year-old patient, who asked not to be named, had not been picked up by the two crew members before and has no history of being aggressive towards G4S staff. He said the message left him distraught.

The story led Conservative MP and former health minister Dan Poulter to say that “the suitability of G4S as a provider of important public services in the NHS and elsewhere needs to be urgently reviewed”.

Norman Lamb, a Liberal Democrat former health minister, called the recording “deeply shocking” and said: “It raises the question as to whether G4S can be trusted to deliver humane, decent and effective services to vulnerable people.”

On Thursday the patient received a letter from the G4S general manager, Tom Maidman, explaining the employees had been sacked following an investigation. “I would like to express how deeply sorry I am that you have been subjected to such an incident and what you experienced is inexcusable,” Maidman said.

“I would like to emphasise that the behaviours the individuals displayed were not in line with the company’s core values and standards and do not reflect the rest of the hard-working staff employed by G4S.

“The type of behaviour displayed on the day in question will not be tolerated in any part of our business. I can confirm that the individuals involved are no longer employed by the company. Please accept my sincerest apologies for any distress the incident may have cause you.”

The patient told the Guardian that despite the two men being fired, he does not feel justice has been done. “This has caused me huge distress – and continues to do so. I still don’t understand why these men were not charged with threatening behaviour or under the Malicious Communications Act. If they had been charged at least they would have been named and shamed. As it is, they retain the privilege of anonymity.”