The government thinks it is on to a good thing. Brexit won a majority in the referendum, so if it carries it out then it will be popular with the voters.
Except that public opinion doesn't work like that.
Take the Iraq War.
A Daily Telegraph article in July looked at new polling by YouGov.
It was no surprise to find that there had been a major shift in opinion on Iraq. In 2003 53 per cent of voters thought the war was right. Now only 26 per cent think it was right.
But more significant - and more worrying for the Conservatives - is another figure.
Today, only 37 per cent of voters think they thought the war was right in 2003, while 43 per cent think they thought it was wrong and 20 per cent don't know.
From which I conclude that if Brexit starts to go wrong - and there is every sign that it will - then the voters will decide that they never wanted it in the first place.
Public opinion can be volatile and voters are more likely to blame politicians when things go wrong than blame themselves.
So if MPs - Tories included - think Brexit will harm Britain then they should have the courage to say so and vote accordingly.
In the words of that great Whig Edmund Burke (Conservatives claim him as their own but do not read him):
Your representative owes you, not his industry only, but his judgment; and he betrays, instead of serving you, if he sacrifices it to your opinion.Later. More detail on YouGov's Iraq polling here.