JUST a day after comparing the UK to superhero comic book character the Hulk, Boris Johnson chickened out of a press conference with the Prime Minister of Luxembourg after he was booed by a handful of protesters.

A clearly furious Xavier Bettel went ahead with the question and answer session alone.

It's understood that after Johnson was booed on his way into the meeting with his counterpart, Downing Street had requested that the press conference be held inside away from the crowds. 

That plea however, was denied. 

Speaking to the assembled press, the Luxembourger leader thanked Johnson for showing up for talks, saying it was important to hear concrete proposals, but he made clear the only proposal on the table is the withdrawal agreement, already rejected three times by Parliament.

The EU would not accept any proposal that undermines the Good Friday agreement, he said.

"I know that the UK Government is unhappy with the Withdrawal Agreement as it stands. That's why I thought it was important to speak to Prime Minister Johnson to get proposals.

"We need more than just words."

There needed to be a legally operational text to work on "as soon as possible" if the October deadline was to be met, he added.

Bettel continued: "Our people need to know what is going to happen to them in six weeks' time. They need clarity, they need certainty and they need stability.

"You can't hold their future hostage for party political gains."

Gesturing to the empty podium where Boris Johnson should have been, Bettel added: "Now it's on Mr Johnson – he holds the future of all UK citizens and every EU citizen living in the UK in his hands.

"It's his responsibility. Your people, our people, count on you – but the clock is ticking, use your time wisely."

The National: Protesters booed Boris Johnson in LuxembourgProtesters booed Boris Johnson in Luxembourg

WATCH: Boris Johnson met with barrage of boos after Brexit talks

Bettel added: "For me I just have one withdrawal agreement on the table and it's the one from last year.

"There are no changes. There are no concrete proposals for the moment on the table. And I won't give an agreement to ideas. We need written proposals and the time is ticking."

Bettel urged Johnson to "stop speaking and act", adding: "But we won't accept any agreement that goes against a single market, who will be against the Good Friday Agreement."

He said "solidarity" with Ireland is "strong" before noting: "This Brexit it's not my choice.

"It's been a decision from a party, a decision from David Cameron to do it. They decide, I deeply regret it but don't put the blame on us because now they don't know how to get out of this situation."

Speaking to Sky News afterwards, Johnson said his "points would have been drowned out" by protesters, and that he didn't think it fair to Bettel. 

The National: Boris Johnson on the balcony of the UK ambassador's residenceBoris Johnson on the balcony of the UK ambassador's residence

The Prime Minister went on to say that the UK had "actually just the right amount of time to do a deal" with the EU before the crucial European summits on the 17th, 18th October. 

"Yes there is a good chance of a deal. Yes, I can see the shape of it, everybody can see roughly what could be done, but it will require movement, and it will require the system by which the EU can control the UK after we leave, the so-called backstop, to go from that treaty, and that needs to happen. 

"So that's a big change that we need to get done, but if we can get that done as I've said before, then we're at the races.

"But as I never tire of telling you, if we can't do a deal by then, and obviously we want to work very hard to do it, but if we can't do it by then, we'll make sure that we can come out of the EU on the 31st of October, deal or no deal."

Johnson’s meeting with Bettel followed lunch with European Commission President Jean-Claude Junker, and EU Brexit negotiator Michel Barnier.