The European Commission on Thursday proposed a back-up plan which aims to ensure, among others, the basic reciprocal air and road connectivity between the European Union (EU) and the UK if the two sides fail to cut a post-Brexit trade deal.

"Negotiations are still ongoing. However, given that the end of the transition is very near, there is no guarantee that, if and when an agreement is found, it can enter into force on time," said European Commission President Ursula von der Leyen in a commission press release.

While she stressed that the commission would continue to do its utmost to reach a mutually-beneficial agreement with the UK, there was now significant uncertainty whether a deal will be in place with just three weeks to go.

The set of contingency measures were designed to prepare for all eventualities, including not having a deal in place with the UK on Jan. 1, 2021.

The main purpose of the plan is to ensure basic reciprocal air and road connectivity between the EU and the UK, as well as allowing for the possibility of reciprocal fishing access by EU and UK vessels to each other's waters.

It proposes that basic air transport will continue for six months provided the UK agrees to reciprocate. The same applies to access for road haulage.

An interim fisheries regulation is put forward to allow continued reciprocal access by EU and UK vessels to each other's waters until the end of 2021, or until a fisheries agreement with the UK has been concluded.

"Readiness and preparedness are now more important than ever. Disruption will happen with or without an agreement between the EU and the UK on their future relationship," said von der Leyen in the commission release.

"This is the natural consequence of the United Kingdom's decision to leave the Union and to no longer participate in the EU Single Market and Customs Union," she added.

British Prime Minister Boris Johnson traveled to Brussels on Wednesday for a meeting with the EU executive chief. She afterward tweeted that both sides had agreed to give negotiators until the weekend to make a breakthrough.

"We had a lively and interesting discussion on the state of play on outstanding issues," von der Leyen said on Wednesday, underlining that the positions of both sides remained "far apart." Enditem