The UK will leave the European Union without a deal unless it makes "positive proposals", the bloc's chief negotiator has warned.

Michel Barnier said the withdrawal agreement between the government and the EU was the best one available given Prime Minister Theresa May's "famous red lines".

They include an end to freedom of movement and to membership of the single market - the European trade bloc which guarantees the free movement of goods, capital, services and labour.

According to Reuters, Mr Barnier told German radio station DLF that if no "positive proposals" are made by Britain "it will be [a] no-deal Brexit".

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"If something changes with the red lines, then we are ready to talk about that," he added.

"We can't make any compromises on the fundamental principles. We can't dilute the single market or split the EU."

Mr Barnier also said the controversial "backstop" - the customs plan to avoid a hard border between Ireland and Northern Ireland if a free trade deal is not reached - could not be time-limited because that would defeat its purpose of guaranteeing no hard Irish border.

Image: Theresa May is meeting trade union leaders about Brexit

"We have to maintain the credibility of this reassurance," Mr Barnier said.

"It cannot be time-limited... It's not just about Ireland."

The European Parliament's Brexit coordinator Guy Verhofstadt reinforced the message that the backstop arrangement could not be tinkered with.

He warned its removal from the UK's withdrawal agreement, which he described as "fair" but "non-negotiable", would see MEPs refuse to ratify the deal.

Mrs May has told MPs she will hold more talks around the backstop as she seeks to get a Brexit deal through parliament.

Hundreds of Irish police officers could be deployed to guard the border if the UK leaves the EU without a deal, the Irish Independent reported.

The newspaper cited a meeting of Police Commissioner Drew Harris with senior staff on Wednesday.

Mr Barnier was due to hold talks with German Chancellor Angela Merkel in Berlin on Thursday.