It is a year since the Conservatives launched their pre-election campaign with a poster of an airbrushed David Cameron, bearing the legend "I'll cut the deficit, not the NHS". At that time, it seemed the party would adopt a safety-first approach to the National Health Service. We welcomed Mr Cameron's pledge to ring-fence spending and to stop the "top-down reorganisations of the NHS", a promise reaffirmed in the coalition agreement in May 2010. No one, from the Tory leadership downwards, hinted at the revolution the government is now preparing to unleash. Here, after the surprise decisions to triple university tuition fees, abolish universal child benefit and raise VAT, is yet another example of this coalition's calculated dishonesty.

Following the publication of the Health and Social Care Bill, alarm is beginning to spread over the biggest reforms to the NHS since its creation. If we are to believe Mr Cameron, the decision to abolish primary care trusts and hand over 80 per cent of England's health budget to GPs will reduce bureaucracy, improve efficiency and empower patients. In reality, it will empower the private sector, introduce an external market and bring about the end of the NHS in all but name.

The requirement for the new GPs' consortiums to commission services from "any willing provider" opens the way for full-scale privatisation of the health service. As our report on front-line Britain (starting on page 24) shows, few GPs feel ready to shoulder this responsibility. A doctor writes: "We have absolutely no idea how we're supposed to do it." In practice, many will transfer responsibility for commissioning to the private sector, creating a conflict of interest as the same private companies become both purchaser and provider. Little wonder that Kingsley Manning of the health firm Tribal has welcomed the reforms as the "denationalisation" of the NHS.

But it is the decision to open the health service to competition law that represents the most pernicious aspect of this bill. To avoid legal action by private firms, the consortiums will be obliged to put all contracts out to tender. Worse, the new NHS operating framework states that providers will be able to offer services to commissioners "at less than the published mandatory tariff price". In other words, the private sector has been given free rein to offer temporary loss leaders, undercutting the NHS. With the health service required to make unprecedented savings of between £15bn and £20bn by 2014, the danger is that GPs will prioritise cost over quality. The limited experiment with price competition during the Major government led to a decline in standards of care, according to research by economists at Imperial College London.

Opposition and scepticism towards the changes extend well beyond the ranks of the trade unions. Most GPs oppose the reforms, as do the Patients Association and the independent King's Fund think tank. Meanwhile, the Commons health select committee, chaired by the former Tory health secretary Stephen Dorrell, warns that the change of policy has not been "sufficiently explained" and the Conservative MP Sarah Wollaston, who was until last May a GP, likens the reforms to throwing a "grenade" into the system.

Since the government's plans were announced, Mr Cameron has struggled to explain them to the public. In the space of one radio interview on 17 January he described the reforms as "evolutionary" but also insisted that "fundamental changes" were needed. The detail has been left to the Health Secretary, Andrew Lansley. Mr Cameron is fond of presenting himself as a chairman rather than a chief executive, but it is he who will bear ultimate responsibility if the reforms precipitate the biggest crisis in the history of the health service.

Aware that its time in office may be short, the coalition is pushing through changes for which it has no mandate and at breakneck speed. We feel the onus is once more on the Liberal Democrats to halt or, at the very least, delay these reckless reforms. Should they fail to act, they will forfeit, as David Owen, one of the founders of the Social Democratic Party, writes on page 30, any claim to be "the heirs of Beveridge".