Dame Vivienne Westwood and Vanessa Redgrave are expected to join thousands of junior doctors and their supporters later as they stage a "masked march" protest over pay and conditions.
The demonstration comes ahead of a 24-hour walkout due to begin on Wednesday, when junior doctors across the country will provide emergency care only from 8am.
It will be the third time junior doctors have taken to the streets in protest at the Government's proposals, which it says aims to improve care over weekends.
Talks between the British Medical Association and the Department of Health reached an impasse over weekend pay rates despite the Government claiming it had made a "significant offer".
According to their Facebook page, organisers are expecting over 3,000 people to turn out for the march on Saturday afternoon, which is due to begin at Waterloo Place in St James before terminating outside Downing Street.
The protesters, who are being encouraged to wear surgical masks, plan to stage a "silent protest" then "burst into voice".
Dame Vivienne, 74, designed a T-shirt for the Wear Your NHS campaign - a play on "We are your NHS" - and both the fashion designer and actress Redgrave are expected to give speeches.
Actors Sir John Hurt and Peter Capaldi have also backed the campaign, whose organisers urged: "Don't let spin doctors exterminate the NHS."