Video report by ITV News Correspondent Angus Walker

Last night, I’d been reporting on the meeting at the UK Ambassador’s Residence in Brussels between Michel Barnier and Brexit Secretary Stephen Barclay.

They’d been joined for their dinner by their respective teams, including Olly Robbins, the UK’s chief Brexit negotiator.

I saw Olly Robbins leave the dinner and walk to his taxi as my cameraman and I were preparing to report live outside for ITV News.

Once we’d finished we returned to our hotel and decided to have a quick nightcap in the bar.

It was then, when we walked into the bar, we realised Olly Robbins was also in the same hotel. He too was having a drink.

He was with two colleagues in the bar and could be clearly overheard by other guests as he gossiped about Brexit, the cabinet and MPs.

He was speaking in such a manner that you didn’t have to listen hard to hear him. But to be clear, I was hearing chunks of their conversation and not every single word.

Olly Robbins with former Brexit Secretary Dominic Raab. Credit: PA

But during that conversation Olly Robbins said that, in his view, he expects the choice for MPs to be either backing May’s deal or extending talks with the EU.

He expects MPs in March to be presented with backing a reworked Brexit deal or a potentially significant delay to Brexit, he told colleagues last night.

“The issue is whether Brussels is clear on the terms of extension,” he was overheard saying. “In the end they will probably just give us an extension.”

ITV News Correspondent Angus Walker reports on Olly Robbins' "extraordinary" comments which he overheard

This is significant. The prime minister has consistently said that we are leaving the EU on March 29th and that she will not engage with discussion about delaying our departure.

We now know her chief negotiator – who works directly for her – appears to be expecting a delay. A delay which she has always said was an option that was not on the table.

Robbins added that he thought the fear of a long extension to Article 50 might focus MPs' minds.

Olly Robbins at a meeting with former Brexit Secretary David Davis. Credit: PA

He suggested: “... Got to make them believe that the week beginning end of March... Extension is possible but if they don’t vote for the deal then the extension is a long one...”

On the backstop, Robbins outlined a strategy to satisfy Theresa May's backbenchers, saying the European Commission would need to agree that the word “necessary” in the Northern Ireland protocol is defined as “necessary subject to the future trade deal”.

At the moment the text of the document says the backstop must “maintain the necessary conditions” for North-South cooperation under the Good Friday Agreement.

It appears that Robbins and the prime minister want the Withdrawal Agreement amended so that the Good Friday Agreement would be less of an obstacle to the backstop being superseded by a new long-term trading relationship between the UK and EU.

What is also striking is how Robbins confirmed that the original plan was for the backstop, which would keep the UK in the customs union, was designed not as a "safety net" for the island of Ireland but as "a bridge" to the long-term trading relationship - which is something the prime minister has always denied.

“The big clash all along is the ‘safety net’,” Robbins said. “We agreed a bridge but it came out as a ‘safety net’.”

These remarks by Robbins are explosive, because they will confirm the fears of Tory Brexiters that he and May always saw some form of customs union membership as the long term ambition for the UK's trading relationship with the EU.

Had it stayed as a ‘bridge’ into a customs union that might have lessened Labour opposition to the deal.

He explained that the current talks in Brussels need to find a ‘way out’ for those who see the backstop as a “trap”.

The talks go on.

A government spokesperson said: “We don’t propose to comment on alleged remarks from a private conversation. The government’s focus is on securing the improvements Parliament needs to pass a deal so we leave the EU on 29th March.”