A panellist on BBC Question Time was applauded by the audience for her “no-brainer” solution to the damage caused by Brexit.
Political commentator Sonia Sodha said the move would be a “quick win” for the UK and make the country richer.
Her comments came as negotiations continue over a new UK-EU trade deal ahead of a crunch summit on Monday.
A woman in the Question Time audience asked the panel what could be done to deal with the “economic damage” done by Britain’s decision to leave the EU in the 2016 referendum.
Sodha, a former columnist with The Observer, said: “The last thing you do as a country with our issues is to put up masses of trade barriers with your closest trading partner.
“That was absolutely nuts, and as a quick win on growth – and it won’t be that quick because we’ve got to renegotiate – we should absolutely be looking to rejoin the single market and customs union.
“It is a no-brainer for us in terms of making us richer, and you and me better off because it’s one of the reasons why we’re poorer at the moment.”
However, Keir Starmer has already ruled out Britain rejoining the single market and customs union – as well as the return of free movement between the EU and UK.
Watch the full exchange below: