Mr Clegg said the Brexiteer was right to suggest “playing for time” by extending Article 50 rather than accepting a transition deal.
Such a transition deal, Mr Clegg conceded, would leave the UK a “vassal state” – something he said Jacob Rees-Mogg was right to be pointing out.
Mr Clegg said he was staggered the debate had reached the point where he, an ardent Remainer still calling for a second EU referendum, was agreeing with hardline Brexiteer Mr Rees-Mogg.
He wrote in the Financial Times today: “I agree with Jacob Rees-Mogg … There. I’ve said it.
“I never thought I would — and I doubt I ever will again — but he is right about one crucial component in the Brexit puzzle: the transition period.”
Mr Clegg said agreeing to EU rules while losing membership benefits was pointless and demeaning for a country of Britain’s size.
He said: “Mr Rees-Mogg correctly observed that it would be more ‘honest’ simply to extend the Article 50 timetable rather than condemn the country to the humiliation of negotiating our departure from the EU having already evicted ourselves from it.
“It is wrong as a matter of constitutional principle — for however long or short a period of time — for a country the size and importance of the UK to become, in effect, a neutered state.”
He said Mr Rees-Mogg and he were agreed only one solution was available: extending Article 50.
This would reassure UK businesses panicked about a Brexit cliff edge as well as allowing Britain to receive EU benefits while still in the bloc.
Mr Clegg concluded: “The conclusion is inescapable: to complete the Brexit negotiations successfully the government needs more time. Mr Rees-Mogg’s legitimate condemnation of what a transition period means in practice now offers a way forward.
“After months of bitter recrimination between Brexiters and their opponents, there is finally the chance for a consensual way forward. Playing for more time is the right thing to do.”