Thanks for the replies. To be honest, I'll give them a single chance to respond favourably. And if their response tries to tell me they won't refund me my money, then I'll just ask my credit card company to start a chargeback. From my perspective a flight cancellation and and an offer only to book me on a different flight to a different airport would constitute a contractual failure to deliver the service I paid for so I'm fairly certain I can get my money back via that route.

But still, I'd consider it outrageous behaviour if they were to actively try to prevent me getting my money back. To be honest its already pretty atrocious to communicate a flight cancellation and a re-booking to a different airport as a "Flight Schedule Change" and provide absolutely no offer of refund or cancellation, in line with my rights.