Thousands of people are expected to join a protest outside Parliament on Sunday as part of a demonstration against the Government's controversial health reforms.
Direct action group UK Uncut said trade unionists, pensioners, comedians including Josie Long and Mark Thomas, and health workers will be among those planning to block Westminster Bridge.
The protest, described as a "spectacular act of mass civil disobedience", is being held just days before the House of Lords debates the Health and Social Care Bill.
A UK Uncut spokesman said: "Yes it will be disruptive and it will stop the traffic, but this is an emergency and if we want to save our NHS we need to shout as loud as we can. No-one voted for this bill, but together we can stop it."
A Department of Health spokesman said: "The principles of our modernisation plans - patient power, clinical leadership, a focus on results - have been widely supported, as reported by the independent NHS Future Forum.
"We accepted all of their recommendations to strengthen the Bill but the most destabilising factor for the NHS would be greater uncertainty and delay of reform to the ultimate detriment of patients.
"We simply won't secure the future of the NHS without this Bill."