The junior doctor at the heart of an escalating row over NHS strike action has warned that the imposition of a new contract could lead to a collapse in morale and an exodus of staff.

Ellen McCourt, chair of the British Medical Association’s junior doctors committee, said that the health service, which faces the looming prospect of Brexit and an ageing population, was already “chronically understaffed” and that the proposed changes risked pushing the service to breaking point.

“The biggest risk with this contract, and also with this dispute continuing, is that doctors will leave the NHS,” said McCourt. “You can’t stretch us more thinly. There needs to be a plan – how are we going to make medicine more attractive to people? How are we going to make people stay in the NHS?”

The BMA announced on Wednesday that it would begin an unprecedented five-day walkout by junior doctors later this month, with further five-day strikes proposed for each month in the run-up to Christmas. Earlier this summer, 58% of doctors rejected a compromise contract deal backed by the then BMA junior doctor leader, Johann Malawana. He has since resigned and been replaced by McCourt.

The strike announcement has divided the medical community, provoking criticism from Academy of Medical Royal Colleges, which brings together doctors’ professional bodies. Many within the BMA are also concerned about the impact the action will have on patients and there have reportedly been ferocious exchanges at meetings where the proposed action was discussed.

McCourt said the greatest risk was that doctors, whose morale is at “rock bottom”, will no longer want to work in the UK if NHS resources are stretched still further. The new contract is designed to make it cheaper to rota more doctors in at weekends.

“I have some colleagues who took time out to work in New Zealand between their first two years of training and their speciality training, and they came back to the UK because they’d always planned on coming back to the UK,” she said. “Now they plan on leaving again. One is a general practice trainee and one is an emergency medicine trainee – our most under-recruited specialities.”

Last year, General Medical Council figures showed newly qualified doctors formed a growing proportion of the thousands of British medics seeking jobs abroad each year. This summer the Institute of Public Policy Research thinktank warned about the threat Brexit would pose to the NHS, stating that the health service would collapse if it were to lose its 57,000 workers who are EU nationals.

The increased number of places for prestigious medical courses offered this summer through university clearing – traditionally the bargain basement for degree places – could be a worrying sign of what may be to come, she said.

Ellen McCourt: ‘You can’t stretch us more thinly. There needs to be a plan.’ Photograph: Sarah Turton/BMA

McCourt added that the strikes could have been avoided, but that when she wrote to the health secretary a month ago outlining the reasons why junior doctors had rejected the new contract, she was ignored. “When he imposed the contract, he said in parliament: ‘My door is always open, I want to be able to address any outstanding problems’, so I took him at his word.”

Health Education England and NHS Employers, who were also addressed in the letter, responded to the points raised – which included concerns relating to part-time workers – but Hunt did not, said McCourt. “I tried two weeks ago to get back in touch with the secretary of state to ask why haven’t we heard anything back and I could only get in touch with his special advisers; I couldn’t get in touch with him. And when we [met] on Tuesday it was very different – it was: ‘Well, you’re proposing industrial action so we haven’t responded’.

“If we’d seen some response or some movement then we could have said, well, the government do want to talk to us, they are willing to make changes without us again resorting to industrial action.”

A Department of Health spokesperson said: “It’s unfair to suggest we haven’t responded to this letter – we resolved two of the issues the BMA raised and gave them a clear timeline of when we would respond on the final two pay-related issues. Despite this, the BMA didn’t wait and announced industrial action. As doctors’ representatives, the BMA should be putting patients first, not playing politics in a way that will be immensely damaging for vulnerable patients.”

The BMA argues the new contract, which is being phased in from the autumn, unfairly affects those who work less than full time, many of whom are women. It also says the terms are damaging to doctors who work the most weekends, which typically includes those who are in areas such as A&E, where there are already staff shortages.

“This contract financially disincentivises less-than-full-time trainees – carers, parents, who are predominately women, in a workforce that is predominantly women,” said McCourt. “It will cost some women more money to go to work than to stay at home.”

McCourt, who has become the focus of press attention following the strike announcement, said that the drastic action was being taken as a last resort. “I would much rather be in a room with the government getting this sorted out than having to make the plans that we’re being forced to make, hearing that the press are hounding my family. I would much rather be talking with the government, with NHS employers to try and get an resolution to this.”