The UK could be left without any flights to and from Europe for a period after March 2019, unless the British government to provides a coherent post-Brexit plan, Ryanair has warned.

On Wednesday (29 March), the budget airline urged the government to make the aviation sector a topic of priority in its upcoming negotiations with the European Union, just hours before Prime Minister Theresa May triggers Article 50 to formally begin the Brexit process.

Ryanair, which has repeatedly expressed itself as in favour of remaining in the EU, said there was a distinct possibility Britain could be cut off from flights to and from Europe for a period of time from March 2019, which is seen as the finish line of the Brexit negotiations.

Among Brexit's numerous implications, the UK will leave Europe's "Open Skies", an international policy which has liberalised the rules and regulations of the international aviation industry to create a free-market environment. As a result, Ryanair said, the government will either have to negotiate a bilateral agreement with the EU to allow flights to/from Europe to continue, or else revert to historical WTO rules.

However, given the latter do not cover aviation, doing so would raise the possibility of no flights to and from Europe until a bilateral deal is agreed.

"Some nine months on from the Brexit referendum, we are no closer to knowing what effect it will have on aviation," said the airline's chief marketing officer Kenny Jacobs.

"It's become worrying that the UK Government seems to have no plan to maintain Britain's liberalised air links with Europe, in the absence of remaining in the "Open Skies" regime.

"The best we can hope for is a new bilateral agreement between the UK and EU, however, we worry that Britain may not be able to negotiate such a bilateral in time for the release by airlines of summer 2019 schedules in mid-2018."

Like all other airlines, Ryanair, which employs over 3,000 UK staff and will carry approximately 44 million customers to and from British airports this year, plans its flights 12 months in advance, meaning there are only 12 months left until it finalises its summer 2019 schedule.

"The UK Government must respond to the airlines and our customers, and put aviation at the top of its agenda when it negotiates its Brexit deal with Brussels," Jacobs added.

"Britain's airlines, airports and holidaymakers need a real and early solution for aviation, or risk Britain being cut off from Europe in March 2019."

The Dublin-based airline has already pivoted growth away from the UK to other EU airports, basing no additional aircraft at its 19 UK airports in 2017 and cutting its growth rate from 15% to just 6% this year.