Britain’s biggest trade union body has called on the Labour government to consider rejoining an EU customs union, reopening a core Brexit fault line as the party grapples with weak growth and rising pressure from its traditional base.

In an interview with the Guardian, Trades Union Congress (TUC) General Secretary Paul Nowak said Labour should seek the closest possible economic relationship with the EU to ease trade friction and support household incomes.

“The government needs to do whatever it can to build the closest possible positive working relationship with Europe economically and politically … up to and including the customs union,” Nowak said.

The U.K. left the EU customs union after the 2016 Brexit referendum, formally exiting the bloc in January 2020 under then-Prime Minister Boris Johnson. Britain remained aligned with EU trade rules during a transition period before fully leaving the customs union on Jan. 1, 2021, when the EU-U.K. Trade and Cooperation Agreement took effect. 

The move restored Britain’s ability to strike independent trade deals but introduced customs checks, rules-of-origin requirements and new barriers for exporters.

Prime Minister Keir Starmer has so far ruled out rejoining the customs union, framing it as a red line while promising a broader “reset” with Brussels.

“We are getting a closer relationship with the EU on a number of fronts, including on trade and the economy,” Starmer told MPs earlier this month, adding: “We have clear red lines in relation to the single market and the customs union.”