Britain will be "fully prepared" for leaving the European Union without a deal, Downing Street has insisted.

British Prime Minister Theresa May’s office was forced to defend its preparations after reports civil servants have been drawing up scenarios for a "Doomsday Brexit" that would leave the country short of medicine, fuel and food.

Mrs May still believes that "no deal is better than a bad deal", and a "significant amount of work" had been done to make sure the UK could cope without a Brexit agreement, Downing Street said.

The Sunday Times reported that models for mild, severe and "Armageddon" reactions to no-deal exits were created by officials, with a source saying that even the severe scenario saw the Port of Dover "collapse on day one".

However Mrs May's official spokesman said: "The Department for Exiting the European Union has said that these claims are completely false.

"A significant amount of work and decision making has gone into our no deal plans, especially as it relates to ports, and we know that none of this would happen."

Asked if that was a "cast-iron guarantee", the spokesman said: "We are planning for all scenarios and we will make sure that we are fully prepared in the event of any eventuality."

But the government had "equally been clear that we will secure a good deal" and it was "in the interests of both the UK and the EU to do so".

Mrs May was due to meet senior business figures in Downing Street on today amid concerns about progress in the Brexit talks.

A promised white paper on Brexit may not be published before the June summit of EU leaders as Downing Street said it was "not putting a time frame on it".

An indication of Europe's concerns about the lack of progress came from Germany's top Brexit diplomat Peter Ptassek, who played down expectations about the 28-29 June European Council.

"Not many are expecting very much now," he said. "If this is so, October would then have to solve all problems [withdrawal, NI, governance, future...] in one go. Odds still unclear."

Mrs May's official spokesman said: "We are working towards reaching agreement in October and the June council is a staging post towards that."

Meanwhile, an influential think tank suggested Britain should be prepared to align itself to EU rules regarding goods exports after Brexit, but is too large an economy to allow the service sector to be a "rule-taker".

Open Europe said Britain should align with existing legislation on goods, citing Switzerland's trade with the bloc as an example of how it can work with a non-member state.

It said Britain's "comparative advantage" lay in services, including the financial sector, and there should be "mutual divergence" in this area.