It remains a shock when a government lies through its teeth – deliberately and outrageously. I resist the idea that politicians are liars by nature: the art of politics and persuasion is difficult and more honourable than it gets credit for. But over the Conservatives' true intentions for the NHS, right from the start David Cameron and his team set out to mislead the public, the clinicians and their own coalition partners.

As parliament broke for half term, regulations for the Health and Social Care Act slipped out – a legal document anyway unlikely to make headlines. The act is a spatchcock confusion of quangos that carefully left most details to be laid out in this dense legalese. But read clause by clause, this document shows how far the act does the reverse of what ministers promised. Commercialisation and competition is written into its key section 75, opening up virtually all the NHS to public tender in a market supervised by Monitor. Secondary legislation is rarely challenged – but this is a final chance for parliament to strike out the obligation of clinical commissioning groups (CCGs) to advertise almost every service to any bidder under EU competition law. It will pass, unless the Liberal Democrats rebel at having been hoodwinked. And they just might.

When the bill was shipping water, the medical professions and many peers so strongly opposed the threat to commercialise the NHS that David Cameron "paused" the legislation. Expecting the Lib Dems to wreck it, he was reportedly surprised they accepted relatively minor amendments. What swung them were public assurances from ministers that seemed convincingly cast-iron.

From the start the plan was misrepresented to the public "as putting GPs in the driving seat", free to commission best services for their patients. The health department was at it again this week, announcing more commissioning groups approved: "All 8,000 GP practices in England will be members of a CCG, putting the majority of the NHS budget in the control of frontline clinicians for the first time."

Clare Gerada, head of the Royal College of GPs, calls that "disingenuous", since all GPs are legally forced to join, yet only a minority of CCGs are led by GPs. Most are not involved, she says, with "barely time to do their day job". She is shocked by the section 75 requirement for every service to be tendered out and advertised on a national NHS website. However satisfied GPs may be with local NHS services, if anything is not put out for tender Monitor can step in to enforce it. As the bill went through parliament, Monitor's role was amended from "promoting competition" to "preventing anti-competitive behaviour" – a change in grammar, not in law, repeated in regulations. That's what the act is for.

Let's reprise the reassurances that soothed Lib Dem fears. The Tory health minister Earl Howe, steering the bill through a rebellious Lords, promised: "Clinicians will be free to commission services in the way they consider best … they will be under no legal obligation to create new markets … this will be made absolutely clear through secondary legislation." But now that legislation makes the opposite crystal clear.

Andrew Lansley wrote to all CCGs: "I know many of you may have read that you will be forced to fragment services, or to put services out to tender. This is absolutely not the case … The healthcare regulator Monitor would not have the power to force you to … You will have the freedom to work with whoever you want to in commissioning services … You will be free from top-down interference." None of that is true, but ministers promised anything, including an "integration" that was never compatible with competition.

Labour will "pray against" the regulations next week to try to strike them out. Andy Burnham says: "The wording is very explicit. It writes EU competition law into the NHS." But also uncomfortably clear in the small print is how many legal foundations were laid by Tony Blair and his health ministers – many now employed in private health. Burnham has clean hands: as health minister he stemmed the slide by returning the NHS as "preferred provider", and would do so again. For decades the private sector has usefully provided the NHS with some services, but compulsory marketising of everything regardless of local need is ideologically propelled vandalism. Jeremy Hunt has barely mentioned the act, speaking only of care, but in this debate he will need to praise raw competition – or lie about it.

Campaigners from Keep Our NHS Public, 38 Degrees, Open Democracy and others urge the Lib Dems to block the regulations. Remember the reassuring letter Nick Clegg and Shirley Williams wrote to their MPs and peers: "We will introduce measures to protect the NHS from any threat of takeover from US-style healthcare providers by insulating the NHS from the full force of competition law." On Monday Lib Dem leaders in the Lords meet Howe: how firm will they be? Baroness Jolly, Lib Dem health spokeswoman, says: "The regulations fail to reflect the assurances or the spirit of the debate on the act." Lord Clement Jones tells Open Democracy: "Earl Howe's statements in the House of Lords appear completely at odds with these regulations." Surely they will not be so easily soothed again?

At first patients may not notice who profits from their services, as private companies hide under the NHS logo. But the change will be irreversible when NHS services atrophy once contracts are let out. The Lib Dems still have a chance to stop this becoming the most indelible legacy of their time in government.