Ryanair is requesting the domestic air license from the Civil Aviation Authority (CAA) to allow them to still fly from within the UK after Brexit.
The UK is expected to leave the EU in March 2019, meaning flight routes could be affected.
The Irish airline is classed as a foreign airline, and CEO Michael O’Leary repeatedly warned that flights could be grounded post-Brexit.
A UK Air Operator's Certificate (AOC) would allow them to still fly between their UK bases in London, Scotland and Ireland.
GettyRyanair flights: The airline is applying for a UK license
Ryanair UK filed an application on 21 December last for an Air Operator's Certificate (AOC)
A statement earlier today confirmed: "Ryanair today (2 January) confirmed that a subsidiary company Ryanair UK filed an application on 21 December last for an Air Operator's Certificate (AOC) with the Civil Aviation Authority in the UK.
"This may be required for Ryanair's three UK domestic routes in the event of a hard Brexit in March 2019."
The airline will still be able to fly abroad with many of their low-fare routes being in Europe.
The UK routes are just two per cent of the airlines revenues.
Express.co.uk has contacted Ryanair for comment.
GettyRyanair flights: The airline needs the license to fly within the UK after Brexit
Earlier this year, Ryanair chief Kenny Jacobs warned that flights could be grounded between the UK and Europe after Brexit.
He explained on Radio 4’s Today programme: “Britain is going to leave open skies as it now stands, we need to see clarity interns of what is going to be the future of open skies, which will mean either a bilateral or not.
“If there isn’t a new bilateral in place, you may have very restrictive or no flying between Europe and the UK for a period.
“And I think it’s clear we’re heading to what looks to be a very ugly divorce at the moment.”
GettyRyanair flights: The Irish airline has bases in London, Scotland and Ireland
The low-cost airline recently made the unprecedented move to recognise the pilot's unions.
For the first time in their 32-year history, they acknowledged the pilots from the IMPACT union following threats of a Christmas strike.
The pilots threatened the Ryanair strike for better working conditions as well as recognition.
The strike was then suspended, to the relief of thousands of Britons who were travelling during the festive period.