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The week of strikes by junior doctors this month will be followed by three more five-day walkouts in October, November and December in England.

The announcement by the British Medical Association comes only a day after it said there would be five days of all-out stoppages from 12 September.

The move escalates further what has become the worst industrial relations dispute in the history of the NHS.

The Royal Colleges said the proposed strikes were disproportionate.

The dates were agreed at a special meeting of union leaders on Thursday.

It came just hours after Prime Minister Theresa May called on doctors to stop "playing politics" in their dispute over the imposition of a new contract.

It means hospitals will see junior doctors stage walkouts from 08:00 to 17:00 BST from:

Monday 12 September to Friday 16 September

Wednesday 5 October to Tuesday 11 October (although the weekend will be covered)

Monday 14 November to Friday 18 November

Monday 5 December to Friday 9 December

The idea of a sustained period of strikes was proposed in a confidential paper drawn up by BMA officials ahead of this week's meetings as a way of maximising the impact of action.

BMA junior doctor leader Dr Ellen McCourt said the government could stop the strikes by calling off the imposition of the contract, which is due to be rolled out from October.

"If it agrees to do this, junior doctors will call off industrial action."

Image copyright PA

The strikes threaten to cause chaos in the lead-up to winter - the busiest time of year for the NHS.

Health Secretary Jeremy Hunt has described the strikes as "devastating news", predicting they would lead to the cancellation of 100,000 operations and one million appointments.

The Academy of Medical Royal Colleges said it was "disappointed" at the prospect of sustained industrial action.

"We know there are genuine concerns about the contract and working arrangements, but we do not consider the proposed strikes are proportionate," it said in a statement.

"Five days of strike action, particularly at such short notice, will cause real problems for patients, the service and the profession."

Katherine Murphy, of the Patients Association, said she was "gravely concerned" about the prospect of five days of strikes, which would have a "catastrophic impact".

"We are approaching winter and that brings with it additional challenges. Combine winter pressures with an already stretched NHS, alongside a series of extended strike action and it will almost certainly result in a NHS crisis.

"Many patients may be very unwell or vulnerable so we cannot predict the distress or pain this will cause to everyone this will affect."

She urged the government to get back round the table and negotiate with the BMA.

The worried patient

Simon Emmet has a kidney stone and is waiting for surgery. He is meant to have the operation in the next four weeks, but is certain the strikes will push it back.

"I can't see that the strikes won't delay my surgery. There are only two people at the hospital that can carry it out, meaning I already have a four-week waiting time.

"I've been to A&E with abdominal pain twice in the last week. I constantly feel nauseous and I'm in constant pain. I have to take very strong painkillers which make me drowsy.

"I work from home as an IT consultant and I have to balance taking enough painkillers so I can work through the pain, but not so many that I'm too dopey to work. Often I end each day in so much pain that I just lie on the floor waiting for the next day's work.

"I'd really like to believe the doctors have the patients' best interest at heart but it doesn't seem right. They've been arguing about this for three years."

But that appears unlikely as the prime minister, making her first public comments on the dispute, gave her full backing to Mr Hunt on Thursday, saying he was an "excellent health secretary".

Ms May called on the union to cancel the strikes, adding that the NHS had "record levels of funding" and "more doctors than we've seen in its history".

She went on: "The government is putting patients first. The BMA should be putting patients first - not playing politics."

Labour leader Jeremy Corbyn said Mr Hunt should stop treating NHS staff as the "enemy".

"What needs to happen now is the secretary of state to get round a table urgently with the BMA and recognise that the junior doctors are the heart, soul, and lifeblood of our National Health Service," he said.

"They are representing all of us in their desire for an effective, good NHS that works for all. I urge the secretary of state to see them as allies and colleagues in trying to develop a good health service - not, as he's tried to portray them, as some kind of enemy."

The imposed contract

Image copyright PA

Basic pay to rise between 10% and 11% on average

System of supplements paid which are determined by how many weekends - those working one in two will get 10% on top of basic salary

Nights to attract an enhanced rate of 37% above normal time

Replaces old system whereby weekend or night work can attract up to double time

First doctors to go on new terms in October with much of the rest of the workforce to follow by next summer

The British Medical Association says it is not fair on those that work the most weekends or part-timers

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The five-day strikes come after junior doctors have already taken part in six strikes this year, including two all-out stoppages.

Industrial action was put on hold in May when the two sides got back round the table at conciliation service Acas.

That resulted in the agreement of a new contract, which BMA leaders encouraged members to accept.

But when it was put to the vote, 58% of medics rejected it, prompting the resignation of the BMA junior doctor leader Johann Malawana and causing ministers to announce once again that they would impose the new terms and conditions.

A new junior doctor leader, Dr McCourt, was appointed and, in August, the committee she leads called for the union's leaders to sanction the fresh strikes which have now been announced.

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