Ryanair will consider dropping UK domestic routes and has warned of a “worst case” Brexit scenario of “no flights” to the EU “for a period”.

The carrier issued its strongest warning yet of Brexit’s implications yesterday, with Ryanair chief financial officer Neil Sorahan insisting: “We need Prime Minister May to say absolutely, ‘We will agree to free movement of people and abide by the European Court of Justice’ [ECJ].”

Sorahan warned: “Brexit will inevitably lead to an economic slowdown in the UK and the EU. The only positive is it will lead to lower fares for customers to encourage them to fly, but will they be able to fly?

“The best case scenario would be for Britain to remain in the EU Common Aviation Area. But to do that Britain has to remain within the jurisdiction of the ECJ and the UK has made clear it won’t accept that, except maybe in the short term.”

He said: “We need certainty as to whether we’ll be able to fly in the UK and whether we’ll be able to fly between the EU and UK.”

Sorahan suggested airlines need to know “a very good part” of any agreement on flying rights “by this time next year” if they are to plan flight schedules for 2019.

Without agreement, he warned: “There could be a period of time when flights can’t get into and out of the UK to Europe.”

Ryanair’s chief financial officer added: “Lots of questions need to be addressed. Will an EU company be able to own a UK company? Could an agreement require [only] majority UK-owned airlines operate UK domestic flights?

“Nobody knows what the final Brexit will look like. It’s very difficult to make plans.”

He said: “In the meantime, Ryanair is pivoting its growth away from the UK. We grew 6% [in the UK] last year and you may see growth lesson as negotiations go on.

“We’ll make a decision on whether we need a UK air operating certificate (AOC) in the next 12 months.

“Our decision may be not to go for a UK AOC and just drop UK domestic routes. It’s not something we particularly want to do, but we could.

“We connect Northern Ireland to Britain and Scotland to London. [But] UK domestic flights are less than 2% of our capacity. It’s a bigger issue for easyJet – 40% of their traffic is intra-EU.”

Sorahan added: “We’re looking at all scenarios at the moment. There may be a UK-EU agreement on flying, but it’s not ratified [in time].

“The worst scenario is that they haven’t negotiated an agreement [by the time the UK leaves], and there would be no flights for a period of time.”

He said: “We know politics moves slowly, and any deal needs the agreement of 27 governments. We have a raft of European elections so a lot of European governments will be distracted.

“The clock is ticking and we need someone to take control of the process.”