They are fighting Tory health secretary Jeremy Hunt's plans to impose new contracts, which would rip up terms and conditions and put patient safety at risk.
To chants of “Hunt must go” and “Save Our NHS” the march snaked down Whitehall, where doctors held in impromptu sit down protest.
Junior doctor Rebecca, from Liverpool, summed up the mood. “We have absolutely no confidence in Jeremy Hunt,” she said. “He's a liar.”
The doctors’ organisation, the British Medical Association (BMA), has said it will ballot its members for industrial action.
Yesterday's demo follows thousands-strong protests last month in London, Manchester and Bristol.
The junior doctors’ revolt is growing.
Niki, from London, said, “There's huge anger about the imposition of the contracts.”
Delegations came from across Britain – and many like Rebecca booked annual leave to attend the protest.
Emily, from Manchester, said, “The demo in Manchester was fantastic.
“I've come down because we've got to make sure the public knows about the Tories’ lies.”
The Tories and the right wing media are pumping out propaganda about “lazy” doctors.
But their fight is about more than just fears their pay could be cut by up to 40 percent.
The new contracts are part of the Tories attempts to bring in “seven day” working.
In reality, the NHS is already a 24/7 service. Hunt wants to smash pay to prepare the health service for privatisation.
“They're trying to cripple the NHS - it's a pathway to privatisation,” said Nicki.
“If doctors are pushed, people will have less confidence in the NHS and it will be easier to privatise."
Doctors work long hours already – and the new contracts would make it worse. Emily explained, “I worked 89 hours last week. But the new contracts would remove the safeguards that make NHS trusts monitor how long we can work.
“My judgement would definitely be worse by the end of it.”
Amy added, “We already work 12 hours without a break because there's no time to take one.”
This would put patient safety at risk. Nicki, from London, said, “In the 1990s safeguards were brought in precisely because of patient safety.
“Tired doctors working 90-100 hours a week would not be good for patients.”
The Tories are desperately trying to stop the doctors from taking industrial action. They know that it could light up a bigger revolt in the NHS.
Naveed, from Liverpool, said, “This is not just about us – but they thought we were an easy target.
“If they get this through then they'll come for the nurses and other health workers.”
Other health workers joined the demonstration with union banners.
Sam, a Unison union member, told Socialist Worker (pc), “I've been going round the hospital talking to workers about the junior doctors.
“You've got band 2 support workers supporting the doctors – that's a real shift and shows the anger.”
Naveed said, “I'd definitely be prepared to take industrial action. No one wants to, but we've been pushed into a corner.
“If one strike doesn't work then we should do it again.”
Sam pointed out that Unison general secretary Dave Prentis said he'd lead a fight over unsocial hours. “We need to join the fight now," she said
The junior doctors’ protests show the growing anger among health workers at the assault on them led by Jeremy Hunt.
Now is the time for the health unions to organise coordinated resistance and strike together to beat back the Tories’ attack.