To Starmer’s left, backbench rebels including Richard Burgon and Dawn Butler backed the push toward a customs union by the opposition Lib Dems. The members of the left-wing Socialist Campaign Group frame their argument around fears Labour will lose voters to other progressive parties, namely the Lib Dems, Greens and SNP, if they fail to show adequate bonds with Europe. Some other, more centrist MPs fear similar.

Labour MPs with a military background or in military-heavy seats also want the U.K. and EU to cooperate further. London MP Calvin Bailey, who spent more than two decades in the Royal Air Force, endorsed closer security relations between Britain and France through greater intelligence sharing and possibly permanent infrastructure. Alex Baker, whose Aldershot constituency is known as the home of the British Army, backed British involvement in a global Defense, Security and Resilience Bank, arguing it could be key to a U.K.-EU Defence and Security Pact. The government opted against joining such a scheme.  

Parliamentarians keen for young people to bag more traveling rights were buoyed by a breakthrough on Erasmus+ membership for British students at the end of last year. More than 60 Labour MPs earlier signed a letter calling for a youth mobility scheme allowing 18 to 30-year-olds expanded travel opportunities on time limited visas. It was organized by Andrew Lewin, the Welywn Hatfield MP, and signatories included future Home Office Minister Mike Tapp (then a backbencher). 

Labour also has an influential group of rural MPs, most elected in 2024, who are keen to boost cooperation and cut red tape for farmers. Rural MP Steve Witherden, on the party’s left, said: “Three quarters of Welsh food and drink exports go straight to the EU … regulatory alignment is a top priority for rural Labour MPs. Success here could point the way towards closer ties with Europe in other sectors.” 

The Not-So-Secret Europhiles (a.k.a. all of the above)

Many Labour figures argue that all of the above are actually just one mega-group — Labour MPs who want to be closer to Brussels, regardless of the mechanism.

Menon agreed Labour camps are not formalized because most Labour MPs agree on working closely with Brussels. “I think it’s a mishmash,” he said. But he added: “I think these tribes will emerge or develop because there’s an intra-party fight looming, and Brexit is one of the issues people use to signal where they stand.”