Ministers have admitted that more than 150 countries have yet to agree to “rollover” EU deals on everything from trade to flights and nuclear safety after Brexit, triggering a fresh accusation of looming “chaos”.

Countries including the US, Canada, Switzerland and Norway will only be free to give consent once the EU releases them to do so, the government has acknowledged – and no date has yet been set.

At stake are more than 750 deals with at least 168 non-EU countries – enjoyed because of EU membership – stretching far beyond trade to airline services, nuclear parts, fisheries, agriculture and data sharing.

Aerospace chiefs have already warned that planes with UK-made parts could be grounded if they lose their recognised safety certificates, for example.

Now the government has confirmed that none of the 168-odd countries have given “clear agreement” to roll over any deals and that there is no date set for asking them to do so.

The UK has agreed that the EU will decide when the process can begin – and Brussels is expected to give the go-ahead only when Theresa May signs a withdrawal agreement.

Those negotiations remain deadlocked over avoiding a hard border in Ireland, the EU having rejected the prime minister’s Chequers proposals for future trade.

Asked to reveal the number of countries which had promised to roll over agreements, the Department for International Trade (DIT) said it “does not hold any information relevant to your request”.

It said it was up to the EU to “notify the other parties to its international agreements” that it was willing for the UK to still enjoy their benefits, adding: “The notification will issue in due course.”

The position was set out in response to a freedom of information (FoI) request submitted by Charles Marquand, a barrister and former Treasury legal adviser, who told The Independent: “We’re now facing a real prospect of chaos.

“Regardless of the type of Brexit we end up with, there is very little time to ensure these third countries with which we have agreements are happy to roll them over.

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“At the very least, you would expect the government to be finding out how these countries will react – but as it turns out, it seems they just don’t know.”

It would take a “legal miracle” to reach agreement with 168 countries by Brexit day next March, given some might have to pass their own legislation, he said.

The admission comes despite the prime minister claiming to have reached agreement to replicate an existing deal with six southern African nations, while on her recent trip to the continent.

In fact, the small print acknowledged the agreement was not “legally binding” and was “without prejudice” to any changes those countries might demand before it was.

The government has acknowledged the risk of a “loss of trade” after Brexit with such countries, admitting they could exploit the opportunity to demand more favourable terms before agreeing a rollover.

An analysis earlier this year found the UK, through EU membership, had 49 agreements with Switzerland, 44 with the US and 38 with Norway – part of the 759, across 168 countries.

As well as potential renegotiation, a further huge headache will be creating a separate ability for the EU to safeguard nuclear material and certify airline parts or pilots’ licences, for example.

Defending its stance, DIT wrote in the FoI response: “The notification will issue in due course and, following this, third countries will be able to confirm their clear agreement to the continued application of international agreements.

“In advance of the notification issuing, a number of countries have already made public statements of support for this approach.