Opponents of the Government's controversial health reforms are to warn ministers that the changes represent the "biggest threat" the NHS has ever seen.

Thousands of nurses, midwives, doctors, physiotherapists, cleaners, porters and other NHS workers will attend a rally in Westminster in a last-ditch attempt to scupper the Health and Social Care Bill.

A psychiatric nurse, speech therapist, paramedic and pregnant mother will join union leaders and politicians in making speeches at the rally, as well as comedian Jo Brand, who once worked as a psychiatric nurse.

TUC general secretary Brendan Barber will say: "The All Together for the NHS campaign is an unprecedented alliance of unions, royal colleges, professional groups, health service staff, patients and members of the public. Together we are speaking up for a publicly-accountable health service, for the values that make our NHS special and for the ethos of public service itself.

"With the Health and Social Care Bill now going through the Lords, it's vital that we make our voices heard. I want the message to go out loud and clear that our NHS is not for sale, not today, not tomorrow, and not ever.

"The Government's Bill represents the biggest threat our NHS has ever seen. It will mean £3 billion spent on change instead of care, NHS patients pushed to the back of the queue by those with fatter chequebooks, and a postcode lottery of provision."

Dave Prentis, general secretary of Unison, said: "The clock is ticking and we are running out of time to save the NHS. Health workers from across the country will make their opposition to the dangerous Health and Social Care Bill heard loud and clear today in London. They know that the Bill will mean the end of the NHS as we know it and they want it to be dropped.

"Introducing competition into the NHS will usher in private companies. They will put profit before patients. Where you have competition you have winners and losers and it will mean that patients are hit as some hospitals close. Taking the cap off the number of private patients that can be treated by a hospital means that those who can pay will go to the front of the queue. NHS patients will face growing waiting lists.

"The royal colleges don't want the Bill, the GPs and health workers don't want it and nor do the public. The Government ignores the groundswell of opposition at its peril. Voters will never forgive, or forget the party that ruins our NHS."

Other speakers at the rally will include Labour's health spokesman Andy Burnham, crossbench peer Lord Owen, whose amendment narrowly failed in its bid to get the Bill studied by a special select committee, Liberal Democrat MP Andrew George, BMA chairman Dr Hamish Meldrum, Unite leader Len McCluskey and Royal College of Midwives general secretary Cathy Warwick.