In the US, airline-canceled or "significantly delayed" flights (as opposed to passenger-canceled) are entitled to a full refund. The airline will not tend to tell you this, and they'll resist quite a bit, but you're legally entitled to one, even on a non-refundable ticket.
Under EU law (this was before Brexit) you are entitled to a full refund if the flight is cancelled by the airline. If the flight is cancelled less than two weeks before departure you are also entitled to compensation of a few hundred Euro.
I actually got a cash refund from Ryanair, although it took a long time and at every stage they recommended I take vouchers that would have expired after 12 months instead.
It's still British law for now. I've not heard that it's planned to be cut in the mass-cut of EU laws, but given that it's pro-consumer it may well be.
Keep in mind UK law. The airline cancelled so the customer can insist on cash refund.
I spent a week or two messaging with BA via Twitter DMs to ensure I got a cash refund, rather than dealing with their website which was steering everyone to vouchers.
https://www.transportation.gov/individuals/aviation-consumer...
UK seems to be the same: https://www.caa.co.uk/passengers/resolving-travel-problems/d...
> If your cancelled is covered by UK law, your airline must let you choose between two options:
> 1. Receive a refund
> 2. Choose an alternative flight