MPs will vote on the Health Bill this week in the House of Commons.
But GP leaders and senior Liberal Democrats warned that grave doubts remain about the potential impact on the NHS if the reforms go ahead.
Fears increased after emails obtained by not-for-profit investigations group Spinwatch revealed DoH officials have discussed plans for private firms to run between 10 and 20 NHS hospitals in a deal worth up to £500m.
The emails sparked claims the DoH had ‘secret plans’ to privatise the NHS.
Unison head of health Christina McAnea said: 'It is clear that behind the scenes the government is planning to privatise the NHS.'
But GPC deputy chairman Dr Richard Vautrey said: ‘I don’t think it’s secret - NHS hospitals are already being taken over by private companies.
‘That is the reality of the world we are moving into - the Health Bill will make that more likely.
‘I think this is one among many concerns that MPs and peers will want to debate and I hope it will convince them that there are still too many unanswered questions.
‘We are encouraging all doctors to lobby their MP over next few days so they are fully aware of the views of doctors as a whole.
‘The BMA is very clear - the majority of doctors have serious concerns with the Health Bill. We want to improve the NHS, but a wholesale review of the current plan is needed, which is why we are calling for it to be withdrawn.’
However, health secretary Andrew Lansley said: ‘Claims that we aim to privatise the NHS amount to nothing more than ludicrous scaremongering. We have made it crystal clear that we will never privatise the NHS.
‘The NHS is also keeping average waiting times low and stable. The vast majority of patients still receive treatment within 18 weeks despite the increasing volume of patients using the NHS over the last 14 months.
‘The reality is that we're giving more power and choice to patients over how they get treated, keeping waiting times low and cutting bureaucracy so more cash gets to the front line. We will not allow these lies to block the progress we want to achieve for patients.’