The head of the third largest trade union in the UK has demanded ending Free Movement is prioritised over retaining European Union (EU) Single Market membership after Brexit.

The stance of Tim Roache, general secretary of the GMB, is likely to pile pressure on Labour leader Jeremy Corbyn, who is backed by the unions but is also currently facing calling from his parliamentary party to keep the UK in the Single Market.

On Thursday, the union boss suggested continued membership could be negotiated while also tackling freedom of movement, which at present is obligatory. The EU, however, has said this is not an option.

Mr. Roache also claimed Britain did not need to stay in the market to retain many of its benefits.

“People, companies, countries in the EU want to trade with the UK – there’s no doubt about that. What we need to do if we’re out of the Single Market is use that as an opportunity for positive investment,” he told the Today programme on BBC Radio 4.

Just over a month ago, the GMB dropped its long-standing opposition to Brexit, acknowledging that the “pay, terms, conditions and job security of British workers” had been “undercut” by Free Movement.

“Time and again we hear from GMB members that they have been told by their bosses ‘if you don’t want to do this job exactly as I say, there are 20 EU workers who will’,” stated a report on Brexit, which the union published in June.

Mr. Roache’s calls come days after it was reported that Mr. Corbyn is considering forcing a parliamentary vote on membership of the market.

The vote would divide the Tories and has been pushed by Labour’s shadow chancellor and Brexit secretary, who insist the possibility of retaining membership should be kept open.

Less than two weeks ago, however, Mr. Corbyn was promising to back the UK’s exit from the market, so his change of heart has caused confusion.

More pressure was piled on Mr. Corbyn Friday, with a key group of allies, including MPs and several other trades unions bosses, publishing an open letter demanding he now backs continued Free Movement after Brexit.

Former shadow cabinet minister Clive Lewis and MPs David Lammy and Geraint Davies joined forces with the general secretaries of the transport union TSSA and Bakers’ Union for the new “Labour Campaign for Free Movement“.

“Migrants are not to blame for falling wages, insecurity, bad housing and overstretched public services”, they claimed, adding: “Migrant workers have been on the front line of fighting for better pay and working conditions.”