The UK will have replicated less than half the international agreements the EU has in place with other countries by Brexit day, the government has confirmed.

Just 43 of the 161 international treaties and agreements currently in place, including 11 aviation deals to allow planes to keep flying to countries such as Canada and the US, have been rolled over.

Also agreed were five nuclear treaties that would enable continuity of energy supplies, the Brexit secretary, Stephen Barclay, said in a written statement. But he admitted: “If the UK leaves the EU without a deal, it will not be possible to complete the transition of all agreements by 29 March 2019.”

The UK benefited from more than 1,000 treaties, said the government, but officials have determined that just 161 of these are essential for a no-deal scenario, including more than 30 trade deals.

In addition to the 43 deals already done, another 21 are “expected to be ready” for transition by 29 March, leaving a further 97 as work in progress. These include trade deals with Iceland, Japan, Liechtenstein, Norway and Turkey.

As an EU member the UK is automatically party to about 40 trade deals with more than 70 countries and Barclay said it was “not the government’s intention to transition all agreements in their entirety”.

Only a handful of “continuity” deals have already been completed, including agreements with Israel, the Palestinian Authority and the Faroe Islands, accounting for just 11% of the UK’s international trade.

Earlier this week, the international trade secretary, Liam Fox said that several more were in the pipeline, including deals with a group of African countries. But some countries were holding out to see whether Britain crashed out of the EU or not before coming to their decision.

A spokesman for DExEU said “good progress has been made on many of the most important agreements”.

These include nuclear cooperation agreements to support the energy industry in the UK and arrangements for the continuation of airline services to countries including the US and Canada, which will be or are expected to be in place.