BRITAIN could be denied a transition period to smooth over its exit from the European Union if deep divisions between the two sides are not cleared up, it has emerged.

Michel Barnier, Brussels’ chief Brexit negotiator, warned the two-year period requested by Theresa May was “not a given” – and insisted time was running out on securing a deal.

It comes as it emerged the UK Government spent almost £1,000 hand-delivering the Article 50 letter declaring the UK’s intention to leave the EU last year.

Two civil servants travelled to Brussels using business-class train tickets costing £491.50 each – despite claims the letter could simply have been sent by email.

Mr Barnier said three “substantial” disagreements remain over the transition, expected to last around two years after withdrawal in March 2019.

Speaking after the latest round of talks in Brussels, he said he was “surprised” by the UK’s stance and insisted it had to accept the “ineluctable consequences” of its own decision to quit the EU.

He warned “there will undoubtedly be a problem” if a breakthrough is not made, adding: “To be quite frank, if these disagreements persist, the transition is not a given. Time is short – very short – and we haven’t a minute to lose if we want to succeed.”

Mr Barnier also warned that checks at the border between Northern Ireland and the Republic will be “unavoidable” under current plans for the UK to leave the single market and customs union.

He confirmed Brussels was currently working to legally define the arrangements that would need to be put in place to avoid a hard border, and said no proposals had so far come from London.

First Minister Nicola Sturgeon insisted that if Northern Ireland stayed in the single market, the case for Scotland also doing so “becomes a practical necessity”. She added: “Otherwise we will be at a massive relative disadvantage when it comes to attracting jobs and investment.”

Mr Barnier’s comments came after Brussels published a position paper which included a plan to restrict access to the single market if the UK fails to comply with the terms of the transition.

The document provoked fury from UK Brexit Secretary Davis, who branded it “discourteous” and “unwise”. But Mr Barnier said he could not understand the “uproar”.

He said: “There is no wish whatsoever to punish. We are trying to draft an international agreement on a solid basis that can be effectively implemented.”

He said the two sides were at loggerheads over the rights of EU nationals during the transition period.

The UK is also demanding the right to object to new rules imposed on it during the two-year period – while also seeking to continue participating in the development of new justice and home affairs policies, Mr Barnier said.

He insisted the EU’s position was “very logical”, but Mr Davis accused Brussels of trying to “have it both ways” over the transition.

Costs released under Freedom of Information show the two officials tasked with hand-delivering Article 50 travelled using the most expensive passenger ticket offered on regular Eurostar services. Standard tickets typically cost just £89-£159 each way.

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The terms of Article 50 of the EU treaties state only that a country wishing to leave the EU is required to "notify the European Council of its intention", and it is understood that this could have been done by email.

Meanwhile, around 70 Tory MPs were named by the website BuzzFeed as supporters of the European Research Group (ERG), an informal alliance of Eurosceptics putting pressure on Mrs May to pursue a hard Brexit.

One of those named – Andrew Bowie, the Remain-voting Tory MP for West Aberdeenshire and Kincardine – told The Herald he had been surprised to be outed as an ERG member.

He said: “The group is just a forum where people have been on talking about Brexit. Yes, with a more pro-Brexit stance than certain other groups of MPs would be, but it’s certainly not been this illuminati-type organisation it’s been made out to be on BuzzFeed.”