The Health Secretary Andrew Lansley is fighting a desperate rearguard action to save his NHS reforms amid pressure to water them down from David Cameron and Nick Clegg.

Mr Lansley is determined not to abandon his plans to transfer 60 per cent of the health budget to GPs and wants to concede only minor changes during the NHS and Social Care Bill's passage through Parliament.

But there are growing signs that he will be forced to go further than that to allay fears that the shake-up could lead to "backdoor privatisation" and wreck Mr Cameron's drive to win the public's trust on health.

Demands for a rethink will grow today when Ed Miliband offers all-party talks on health reform – but only if the Government ditches the Bill first. Speaking to the RSA think-tank in London, the Labour leader will attack the "chaos" over the reforms and say the way they have been handled is a "disgrace". Mr Miliband will say: "This is a direct consequence of a coalition based on power, convenience and ambition rather than values."

Downing Street dismissed speculation that a U-turn was on the cards and denied legislation had been put on hold. A spokesman said: "The Bill has now successfully finished committee stage in the Commons and there is a break before it moves to the Lords. We have always been prepared to listen. We will also stop Labour's approach of giving preferential deals to the private sector."

However, Mr Cameron and Mr Clegg will mount a campaign to "sell" the reforms to the public and health professionals – a move which reflects their concern that Mr Lansley has not explained the shake-up well.

The Prime Minister and his deputy will also discuss possible changes to the Bill. These include not forcing all GPs to take on responsibility for commissioning by April 2013 as originally planned; tougher safeguards to prevent private firms "cherry-picking" NHS services; and ensuring that new GP commissioning boards that will replace primary care trusts are accountable.