THERESA May was, yet again, calling for unity last night, while addressing the 1922 committee of backbench Tory MPs. She has already succeeded in uniting the party. Unfortunately for her, it’s not the EU Withdrawal Bill that has brought them together, but their shared conviction that the Prime Minister is rubbish at her job.

Although that judgment is undoubtedly correct, and shared by party members – a survey for Conservative Home last week found that two-thirds of them wanted Mrs May gone before the next election – she was still right to urge MPs to fall into line.

One might object, indeed I do object, to the fact that they have not much idea of what it is that they are voting for, but then it is evidence of the Prime Minister’s uselessness that she appears to have very little idea what she is for in general, let alone spelling out what she intends to achieve by way of a Brexit settlement. There is, however, not much that can be done about that over the next two days.

Even so, there are several clear reasons for them to back Mrs May. The first, never far from the thinking of any MP, is that it is necessary to save their own necks. The second is the practical point that implementing Brexit was in their manifesto. The party would be entirely within its rights to withdraw the whip for any MP who chose to rebel. As it happens, the second and third readings of the EU Withdrawal Bill saw not a single Tory vote against, so it would be peculiar for anyone to rebel now.

What’s under discussion today and tomorrow is, in any case, not about the decision to implement Brexit. Quite apart from the fact that the referendum was the single largest popular vote for anything in the history of British democracy, it was overwhelmingly carried by the Commons in the earlier vote to trigger Article 50, without a single amendment and with a majority not far short of 400 votes. Only one Tory (Ken Clarke, of course) voted against.

The EU Withdrawal Bill is about legal continuity; since it involves repealing the European Communities Act of 1972, which provides the authority for EU law to have force in the UK, it is necessary to transpose some 20,000 pieces of legislation into domestic law.

This is essentially a piece of housekeeping. It doesn’t tell us anything about what kind of settlement we are aiming to reach with the EU (just as well, since, as I say, there’s not much indication that anyone in the Government knows what they want, let alone whether they have any chance of achieving it). Nor does the bill commit anyone to anything, other than ensuring that, while ending the supremacy of EU law, exactly the same provisions and regulations formulated during our period of membership remain in place, at least for now.

It was always evident that, to introduce Brexit, some form of “Great Repeal Bill” would be needed, even if Westminster were later to decide to change the degree to which English and Scottish legislation and regulation correspond with that of the EU. It ought to be entirely uncontroversial if you accept, as the country and the Commons already has, that we are going to implement Brexit.

The only reason that it is not is because of the amendments introduced in the Lords. These are, bluntly, mostly pointless except as wrecking manoeuvres. Some, such as Lord Kerr’s amendment to keep the UK in the customs union and Lord Alli’s, which calls for us to remain in the EEA, are explicit attempts to reverse Brexit. Others, such as the amendments on environmental rules and continued membership of some EU agencies, have either been accepted or are already dealt with by proposed legislation elsewhere. The proposal for parliament to have a “meaningful” vote is an especially pointless piece of flag-waving, since the Government has already announced its intention to write a vote on the final deal into the legislation.

But there is a reason why the vote will only be on whether to accept the terms which we end up with by March next year, or leave without a deal, which is much the same as the reason everyone disagrees on what kind of deal they’d like to see. And that is that you can’t present a whole range of different options – Norway minus, Canada plus, Ukraine market-style, Czech pre-accession terms, Efta light, and so on.

The existence of those deals provides plenty of evidence that the EU, despite its protestations to the contrary, is very much in the business of cherry-picking. But while the Government – if it ever gets its act together – might want to investigate any or all of those options, it will have to end up by settling on one arrangement, and then try to sell it to the EU.

That may, to the horror of some Brexit diehards, involve a period of transition, or it may not. It might involve compromises on free movement, or the need to continue adhering to EU regulations. What it won’t be is a choice of several of those – and it definitely won’t be the amendment proposed by the Labour frontbench “to ensure the United Kingdom has full access to the internal market of the European Union”, not least because there’s not a hope in hell that the EU would ever agree to such a thing.

The fact that the Government isn’t making a clear case for what it wants is a worry, and the fact that it seems to be making a poor job of attempting to secure it in the negotiations is more worrying still. The most sensible position would be to accept compromise where it offers an advantage, which broadly speaking means trade in goods, and to reject it where it conflicts with our interests, which broadly means in services, where the UK has much the better hand.

But in the end the choice will be between what is possible. That means either endorsing any deal that can be hammered out, or leaving without one. Since we don’t yet know what we’re being sold, attempting to overturn this bill would do nothing other than sabotage the democratic decision made by the referendum, the general election result and the overwhelming vote already taken by the Commons.