Andrew Adonis, the Labour peer and chair of the National Infrastructure Commission, is under fire for remarks made in an interview with The House magazine in which he compared Brexit to Britain’s decision to appease Adolf Hitler in the 1930s.

A small horde of Brexiteers have come out to condemn the remarks. Former cabinet minister Iain Duncan Smith has said that the comments are “deeply offensive”, adding that “most of the British people” will agree that the remarks are wrong. Another Conservative MP, Peter Bone, has said that Adonis “should be fired” from his post as infrastructure chair, while Steven Woolfe, formerly of Ukip, has said it was “truly disgusting” to suggest “leaving the EU is the same as Appeasing Hitler, Nazism and genocide”.

Slight problem, though. Here’s what Adonis actually said:

“My language is usually pretty subdued in politics but anyone with a historical sense – and I’m a historian – recognises that leaving the economic institutions of the European Union, which have guided our destiny as a trading nation for half a century, is a very big step and the importance can’t be over-emphasised. To my mind, it’s as big a step that we’re taking as a country as decolonisation in the 1950s and 60s and appeasement in the 1930s. We got it right on decolonisation; we got it wrong on appeasement and I think we’re in serious danger of getting it wrong in the way that we leave the EU.”

What Adonis is actually saying is that Brexit is among the biggest and most significant things the United Kingdom has done in the post-war period.

There’s a reasonable criticism to be made of Adonis here: the first is of course that the United Kingdom joining the bloc in the first place was equally big and significant. The second is that actually, Britain shedding its empire was a far smaller deal, not least because the choices taken were so driven by external forces – lack of money, lack of domestic political will – that the decisions made by Clement Attlee,Winston Churchill, Harold Macmillan and Harold Wilson were so constrained that while it was a significant period, it wasn’t a period of significant policy choices. (In fact, many of the choices around decolonisation were set by the decisions made by British politicians during and before the Second World War, rather than decisions actually made in the 1950s and 1960s).

The undeniable truth is that the way Britain handles its decision to leave the European Union – or perhaps, the path that Britain takes to reversing its decision to leave – is going to shape the coming decades in a way that no election and no issue, other than climate change, will.

That’s the insight that a group of Conservative MPs, widely mocked by the right and the left when it emerged that they were willing to risk a Labour victory at the next election if they could secure their preferred Brexit option, have got, as has Adonis. But terrifyingly few politicians on either side have grasped the enormity of what Brexit means.