Forget the airline. Section 75, chargeback and ATOL are where the money is.
Check your flightWorth saying plainly. When an airline enters insolvency, a passenger holding an EU261 claim becomes an unsecured creditor, which is the back of a long queue behind lenders, leaseholders and staff. Most unsecured creditors in an airline failure recover nothing at all.
So do not spend weeks writing letters to an administrator. Put the effort into the three routes that actually work.
This is the strongest one by a distance. Under section 75 of the Consumer Credit Act, your credit card provider is jointly liable with the retailer for the whole purchase, where the item cost between £100 and £30,000.
Crucially, you only need to have paid part of the cost on the card for the whole amount to be covered. Even the deposit is enough. Claim from the card company, not the airline, and they cannot decline on the grounds that the airline has ceased trading, because that is exactly what the protection exists for.
Not a legal right like section 75 but a card scheme rule, and it works often enough to be worth doing. You are asking your bank to reverse the payment because the service was never provided.
There is a deadline, usually 120 days from the date you should have flown, and it is strictly applied. This is the one to act on first, because unlike the others it expires.
If you bought a flight-inclusive package from a UK operator, it should be ATOL protected. That covers getting you home if you are already away, and refunding you if you have not travelled. Check the certificate you were sent at booking rather than assuming.
Travel insurance may also cover scheduled airline failure, though this is frequently an optional extra rather than standard cover. Read the policy before you assume it is there.
Chargeback first if it applies, because it is the one with a deadline. Section 75 next, since it is the strongest. ATOL and insurance alongside. The administrator last, and only for completeness.
Check a claim against an airline still flying