The EU has warned European fisherman that they will have to ask Britain for permission before spreading their nets in its waters in a 'no deal' Brexit scenario.

In a letter published on Monday, officials in Brussels said there was "considerable uncertainty" about the terms of post-Brexit trade, and urged fishermen to take into account "legal repercussions...which need to be considered when the United Kingdom becomes a third country [non-EU member]."

"In accordance with international law of the sea, fishing vessels wishing to engage in fishing activities in waters under the sovereignty or jurisdiction of a third country are required to obtain a fishing authorisation from that third country," the letter continued.

EU fishermen who wished to land and sell their catch at UK ports would also need to follow the rules and regulations of the UK, the letter said.

The stark terms would apply if the UK crashes out of the bloc with no transition period or free trade agreement, which is unlikely at this stage in the negotiations.