The build-up to the euro has just been too damned painstaking

The Eurosceptics are singing in their baths again. Tomorrow is the 10th anniversary of Britain's exit from the Exchange Rate Mechanism (ERM), and already the former chancellor Norman Lamont has cited the disaster of membership as a reason why Britain should never join the euro. Michael Howard, the Shadow Chancellor, will perform on various media outlets today to make the same point. Tomorrow some of the newspapers will have another blast. They are almost grateful for the hated ERM. It provides them with such blissfully discordant melodies.

Very quickly the ERM has acquired mythologies – great big distorting ones. Britain's departure was a moment of such high drama that most of us can recall precisely where we were when we heard the astonishing news (as ever, I was at the heart of events, reporting the Liberal Democrats' conference in Harrogate). Yet the complicated details of the drama soon became hazy. What really happened? Why did it happen?

Through the mists stride Mr Lamont et al, with a single message: at least we escaped from the nightmare of the ERM 10 years ago; if we join the euro, we will be trapped in it for ever. The message gains credence because of the seemingly relevant echoes from that traumatic episode.

The first echo relates to the build-up to entry. Margaret Thatcher used to famously proclaim that Britain would join the ERM when the "time is right". On the surface, this is not greatly different from the Government's position now. It plans to join the euro when it is in Britain's economic interests to do so. Both statements sound firm and emphatic, but actually raise a thousand questions. There were also tensions between Mrs Thatcher and her chancellor Nigel Lawson as there have been between Tony Blair and Gordon Brown. Here we go again, only this time we are walking towards an even bigger disaster.

Oh no we're not. The parallel between then and now ends abruptly at this point. There was a fatal fault line at the top of the Conservative government when Britain joined the ERM. Mrs Thatcher was opposed to joining, while Mr Lawson, supported by the foreign secretary, Geoffrey Howe, took precisely the opposite view. Roughly translated, what Mrs Thatcher meant by "we will join when the time is right" was "we will join if those two awkward bastards, Lawson and Howe, manage to drag me in shouting and screaming". As it turned out, those two awkward bastards failed in their quest. It was John Major as chancellor who finally persuaded Mrs Thatcher to give the thumbs-up at a time when she was politically unpopular and needed a cut in interest rates. For reckless, short-term reasons, Britain joined at the wrong rate and at the wrong time.

Now there is no basic divide between Mr Blair and Mr Brown over the euro. They are in agreement about the need to join. They might have an almighty row over the timing of entry, although I take the minority view that even this is unlikely. Indeed, there are some signs that they are already working closely together on this.

Nor will entry to the euro be sudden, taken for hopelessly short-term reasons. The preparations have been painstaking, almost too damned painstaking. Already the Treasury's assessment of the economic tests runs into hundreds of pages. You can read some of it on the Treasury's website, although you will need to lie down in a darkened room afterwards.

When Britain joined the ERM, she was like a schoolchild rushing into an exam without any revision. Now, in preparing for the euro, Britain is a sweaty, swotting pupil so immersed in revision that she might forget to take the exam.

The bigger myth – about being trapped eternally in the euro – involves a clever sleight of hand. With a single leap, we move from the image of a sunny Britain liberated from the ERM to a country cowed by the never-ending darkness of the single currency. The leap ignores the fact that the ERM was an entirely different entity from the euro. The mechanism was a dream for speculators, allowing them to prey on one currency, and then another. This is what they were doing when Britain was forced out. They cannot make hay in the same way with a single currency. The euro, being a single currency, eliminates speculation between currencies.

So what can be learnt from that unforgettable day when I was listening to a Liberal Democrat debate on rural post offices? There is a specific point. Those who are opposed to the euro have few popular advocates, but they have plenty of populist arguments. The notion that we will be trapped in the currency is one of them. The vivid accessibility of these arguments cries out for a response, made loudly and often. So far, all we get from the Government is that it will join the euro if the economic tests are met – hardly the stuff to rouse the passions.

The build-up to a possible war with Iraq has postponed again the time when Mr Blair can place his persuasive focus on the euro. Worse than that, the build-up reinforces prejudices against "Europe". It is surely no coincidence that the newspapers supporting the Blair-Bush position on Iraq most ardently are those that are scathing about Europe and the euro: President Bush and Mr Blair stand up to tyrants, unlike those hopeless Europeans, the papers scream simplistically. One of the Prime Minister's more substantial achievements is the close relationship he has established with other EU members, but he tends to do this on the quiet. His relations with the US are heralded with trumpets blaring.

This does not mean that Mr Blair is going cold on the euro. I sense that the opposite is the case, that he is more determined than ever to go ahead with a referendum during this term. It does mean that he has a massive task of persuasion on his hands, and he needs to get persuading before it's too late.

There is also a broader point. It is easy to forget that, before the ERM disaster, Mr Major was a popular prime minister, winning a general election against considerable odds in 1992. His popularity was based largely on a perception of competence after the merry-go-round of Mrs Thatcher in her final phase. When a single issue destroyed that reputation, he had nothing left to cling to, no wider sense of purpose or direction. This government's second term needs to be about much more than a war that may not even take place. Otherwise it, too, will start to drift.

There are lessons from the 10th anniversary of quitting the ERM, some big lessons. It is just that they are not the ones that will be proclaimed by the Eurosceptics over the next few days.