What would it take for Britain to rejoin European Union?

The foreign secretary told the News Agents that leaving the EU “badly damaged our economy” and admitted that there would be benefits to rejoining the bloc.

Mr Lammy, asked whether he would like to see Britain rejoin the customs union, said: “That is not currently our policy. That’s not currently where we are.

“But you can see countries like Turkey with a customs union seemingly benefiting and seeing growth in their economy, and again, that’s self-evident.”

He added: "It’s self-evident that leaving the EU badly damaged our economy, took us out of an important marketplace and created serious friction.”

A growing list of Labour MPs are supporting the rejoining of the union after the 2016 referendum which led to Brexit being fully achieved by the Boris Johnson administration.

Health secretary Wes Streeting has also demanded Labour undo "the economic damage done by Brexit" but no government has yet put a u-turn into policy.

The closest we have had is when then-Liberal Democrat leader Jo Swinson made a return to the union a party policy ahead of the 2019 election, but only won 11 seats and lost her own.

What would Britain need to do to rejoin the EU?

If the UK applied to rejoin the union, it would need to re-apply and have its application terms supported by every one of the 27 member states.

Brexit was an unprecedented action for an EU member state and there was no readmission clause, which means that Britain would need to apply like any other European country.

Seeking entry to the union is a tricky political task and can take years to secure, especially with leaders having become stricter about entry since the UK joined in 1973.

On the one hand, British politicians would not need to hold a referendum if they decided to go back into the bloc. And as a previous member, there might be fewer concerns from members.

However, other European nations would likely be skeptical of a re-entry bid, and might look to punish Britain for having left already.

It is very unlikely that the UK would be able to enjoy the same veto right as old, which saw the country refuse the Euro currency and Schengen zone.

Could Britain rejoin the European Customs Union?

While there is no serious talk of a fully-fledged re-entry into the EU, Labour is said to be considering a return to the European Customs Union trade bloc.

On Tuesday, 13 Labour MPs backed a Lib Dem push to back such a policy in the Commons, although the move failed and Sir Keir Starmer said it is not the government’s policy.

Labour peer Harriett Harman told Sky: "In the run-up to the election, Keir Starmer made it quite clear that, if he was in government, he would not be rejoining the single market or rejoining the customs union."

The prime minister is said to have called the idea a “red flag” in an interview this week.

A spokesman commented: “As the Prime Minister set out in the House, we have now signed a series of trade deals that are beneficial to working people, the best trade deal any country has got with the US. We did not unpick that in order to join a customs union.”

Baroness Harman did, however, not rule out Labour looking to consider elements of the customs’ union benefits.

She added: "I think we might get into a little bit of that with the customs union, because we're not rejoining the customs union, but we could have a customs union which is better - i.e. elements of it, which smooth the path of better trading relations."