REVEALED: Labour planned to sell out UK fishermen MONTHS ago but Keir Starmer could be plotting greater Brexit betrayal

However, as the UK continues to "reset" its post-Brexit relationship with the EU, an arrangement compared to the customs union remains on the table for future negotiations.

The Pan-Euro-Mediterranean Convention, which stretches from Morocco to Lebanon, is looking to expand its membership.

Earlier this year, the UK joined a growing list of prospective partners - alongside Syria, Libya and Iraq.

Despite not appearing in the recent "reset" accord, speculation about the UK joining the bloc emerged at the same time as the groundwork had been laid for Starmer to "sell out" fishermen and agree to a Youth Mobility Scheme.

In the months leading up to the summit, Facts4EU , in conjunction with UK Fisheries Campaign (UKFC), warned that Starmer was planning to hand over UK access to EU fishermen.

In fact, the think tank points out that he was left with no choice as the EU first drew red lines over fishing rights four years ago, so the PM was facing a capitulation once the fishing agreement came back up for renewal.

However, a more sweeping overhaul of Brexit could be on the cards. Speaking in January, EU trade chief Maros Sefcovic said: "A Pan-European [customs] area is something we could consider."

The UK Government even reportedly started consultations with business over the benefits of the PEM plan that could help cut red tape and improve trade.

However, No10 stopped short of labelling the potential agreement a customs union - which has long been a red line for the Government.

"The arrangement that's been discussed is not a customs union," a No10 spokesman said.

"Our red line has always been that we will never join a single market, freedom of movement, but we're just not going to get ahead of those discussions."

Chancellor Rachel Reeves went further, indicating she was “happy to look” at the prospect of the UK joining the scheme with Europe.

She said: “It was really interesting to see Maros Sefcovic this week suggest the UK might be welcome in that pan-European and Mediterranean customs framework.

“We are absolutely happy to look at these different proposals because we know that the deal that the previous government secured is not working well enough.

“It’s not working well enough for small businesses trying to export, it’s not working well enough for larger businesses either.

“We’re grown-ups who admit that, whereas the previous government said there were no problems at all.

“And where there are constructive ideas we are happy to look at those, as long as they’re consistent with the red lines we set out in our manifesto.”

But Brexiteers warned at the time that such an arrangement risks "undoing Brexit by the backdoor".

Shadow Business Secretary Andrew Griffith said: “This scheme is not the silver bullet to growth the Government thinks it is.

“Whenever Labour negotiates, Britain loses. So, we need to make sure they don’t surrender important assets like our fishing rights.

“We must avoid undoing Brexit by the back door by aligning with the EU’s low-growth model.”

GB News has approached the Cabinet Office for comment.