A fresh warning on the negative impact Brexit will have on aviation has been delivered by Ryanair boss Michael O’Leary.

O’Leary has repeatedly claimed that flights between the UK and continental Europe are likely to be grounded in April 2019 in the event of a failure to strike a Brexit deal.

Ryanair has already started warning on passengers’ tickets of the risk that flights from April 1, 2019, could be cancelled.

To keep his aircraft flying, O’Leary will need to demonstrate to European regulators that a majority of his investors are EU citizens.

At present, 56% of its shareholders are European, and within that about 20% are from the UK.

He is examining a number of ways to give incentives to non-EU investors to dump Ryanair shares, the Sunday Times reported.

Europe’s largest low-cost carrier already has a rule stating that any shareholders based outside the EU can sell stock only to European investors.

Airlines are entitled to impose such restrictions under their articles of association to maintain their right to fly under international treaties, which depend on an airline’s legal nationality.

If O’Leary cannot persuade investors to cash out, he will force a sale.

“If you don’t do it, we will sell them on your behalf and remit you the money,” he was reported as saying.

The Irish airline has applied for a British operating certificate to continue its domestic UK flights. O’Leary admitted that rules requiring European airlines to be majority owned by European shareholders are a “challenge”.

He accused Willie Walsh, chief executive of British Airways owner International Airlines Group, of “ducking” the ownership issue raised by Brexit, reiterating his claim that it will force IAG to sell Aer Lingus and Iberia.

IAG refuses to say what percentage of its shareholders are European.

“Willie keeps kicking the can down the road and saying, ‘It’ll be all right on the night,’ said O’Leary. “It won’t be.”

Budget carriers such as Ryanair and easyJet have flourished in Europe’s liberalised airspace, which was deregulated in the 1990s when barriers to flying between its countries were torn down. Airlines such as British

Airways also rely on the open skies deal that allows flights between the EU and US.

O’Leary said failure to replicate this deal when Britain leaves the EU would be likely to halt flights, albeit for “a week or a month”.

“There’s every likelihood that there is going to be the prospect of no flights on the first of April next year,” he said.

“Ultimately there’s going to be a disruption to flights, because that’s the only way you’re going to get the British public off its arse to realise that this is a mess.”

He accused transport secretary Chris Grayling of having “no plan whatsoever”.

Grayling has said it is inconceivable that flights will be grounded, a view shared by Ryanair’s UK rival easyJet which has taken steps to become ‘Brexit proof’ by amending its articles of association to ensure it can fly both in the UK and EU after Brexit.