A deputy chief constable has warned that budget cuts are harming the mental health of frontline police after one of her officers, who once boasted the highest arrest rate in the UK, resigned following a breakdown.

Sgt Ali Livingstone of Suffolk police was nicknamed Robocop by his colleagues after arresting 524 people in 2009. But after suffering a significant mental breakdown last year, followed by post-traumatic stress disorder (PTSD), depression and anxiety, he has decided to leave the force.

He said: “I went from being the UK’s top arresting officer to being so troubled by what I’d seen and done in the line of duty that I’ve had to walk away from the very job that defined me.”

Livingstone, 36, who is writing a book about his experience, said his PTSD was not linked to a single incident but the “cumulative effect of being exposed to trauma all day, every day”.

Suffolk police’s deputy chief constable, Rachel Kearton, paid tribute to Livingstone’s bravery in talking about his mental health problems and said she hoped it would encourage other officers to come forward.

But she also warned financial pressure was increasing the workload and stress on officers and hampering forces’ ability to help burned-out police.

She said: “Once upon a time when there had been a crisis I would be able to give [officers] some respite by taking them away from the frontline. That is no longer an option because of the increased demand that we are dealing with and the stretch on the resources.”

She said cuts meant police were increasingly “picking up a number of issues from other agencies that we didn’t have to deal with before”. These include filling in gaps in the health service by taking vulnerable members of the public to hospital.

The Police Federation chair, John Apter, said Livingstone’s decision to quit illustrated a wider problem. He said: “This is happening far, far too often now within policing, where hard-working, dedicated officers who still enjoy the job are being forced to leave because they have been ground down by the relentless pace of policing in the current climate.”

He added: “DCC Kearton is absolutely right – we are the service that can never say no and already-stretched officers are now increasingly forced to deal with incidents including mental health crises because other agencies are either closed for the day or subject to the same austerity cuts that we have suffered.

“But it is precisely because we are a 24-hour emergency service who are there when other agencies are closed that police officers are becoming broken; they need to be able to step away from duty when they are ill or stressed, and be given proper time to recuperate in the right environment, supported by healthcare or other appropriate professionals.

“They need adequate time to rest. Police officers are not robots – they are human beings who, despite the uniform they wear and the training they undergo, have their limits.”

Livingstone praised Suffolk police for the mental health support they provided after his breakdown and he singled out Kearton for thanks.

Kearton said she would welcome Livingtone back to the force “without hesitation”. She added: “I would have loved for him to stay but it has to be what’s right for him. There are time when people need a break and when people need to leave.”

She added: “Mental health is something that we all need to talk more about. The secret is identifying where things are not right and dealing with them as far upstream as we possibly can before they become major issues.”

She emphasised that the performance of officers has never been measured on the number of arrests they make. “Ali was recognised through a number of awards for the quality of his work. That is far better than counting arrests.”