David Cameron begins the fight to save his NHS bill on Monday by convening a summit of health practitioners to look at how to implement his health reforms.

The Downing Street round table, likely to be attended by the health secretary, Andrew Lansley, has already experienced controversy because some professional groups claimed to have been excluded owing to their hostility to the bill.

Cameron has said little in detail about the health reforms since the Conservative Home website called for the bill – which is in the Lords – to be dropped, and claimed at least three cabinet ministers were urging that it be shelved.

The prime minister is determined to ride out the criticism,but knows he has to win back alienated health professionals.

His aides said Cameron was not planning a second pause on the bill and was focused on getting the measures on to the statute book by the end of spring.

The Health Service Journal, which broke the news of the summit, claimed a number of professional groups were angry over who had or had not been invited.

No 10 declined to give details of attendees, but the list is thought to include the presidents of some of the royal medical colleges, NHS Confederation chief executive, Mike Farrar, and British Medical Association chairman, Hamish Meldrum.

It indicates the government intends to press on with implementing its health bill rather that discussing dropping it or making significant changes.

The Academy of Royal Colleges chair, Sir Neil Douglas, wrote to the Royal College presidents , saying: "Some of you will have been invited to a meeting with the prime minister on Monday. This is being titled as a meeting to discuss implementation of the NHS reforms which would indicate where the government is coming from."

He added: "Just to clarify, this is not the meeting between the colleges and the PM that many of us discussed three weeks ago in BMA house but is a Downing Street initiative. We are not yet clear of the invitation list but it appears to be selective and definitely broader than the colleges."

The chief of the Royal College of General Practitioners, Clare Gerada, confirmed her organisation had not been invited. The colleges of radiology and pathology have also not been invited.

However, the meeting will be an opportunity for Cameron to gauge the source of the controversy surrounding the bill and how readily it can be overcome. He is bound to face calls to drop the third part of the bill that focuses on extending competition, a position recently adopted by the Liberal Democrat peer Lady Williams to the surprise of some senior Lib Dems.

Aides to Nick Clegg are aware they are in danger of loyally defending a bill as part of the coalition agreement only to find the Conservatives retreat at the last minute.

Andy Burnham, Labour's shadow health secretary, said: "This has all the hallmarks of an event thrown together in a last-ditch desperate bid to shore up collapsing support for the bill. It would appear to be so last-minute that a number of important organisations have been left off the invite list, or maybe it's because the PM wouldn't like what they've got to say.

"It's a sure sign of a prime minister who is no longer listening and putting his political pride before the best interests of the NHS."

News of the meeting came as the number of signatures on an e-petition on the government website calling for the bill to be dropped rose above 120,000.

It is required that any petition with more than 100,000 signatories has to be referred to the backbench business committee for consideration for Commons debate. But there have been a large number of health debates, and indeed Labour has called a debate on Wednesday to urge the government to publish the national risk register .

Ed Miliband made the claim on Friday that he will make the future of the NHS the defining issue of the general election in 2015. It caused surprise that Labour could know the issue that will define an election three years away, and it also risked suggesting Labour was not prepared to fight the election on the economy.