If you can travel back on tues instead of mon then you can book with thomson as they have flights on tues. Otherwise, you can book the return from Corfu through any travel agent, you could ask at the airport when you land if it is at a time when the airline offices are open. It should not be too much of a problem booking the return from Corfu if you are only looking for 1 seat and you are fairly flexible re. airports. This would be a problem at the end of October - half term and workers returning to UK at end of the summer. Other options (but time consuming) are a domestic flight to Athens with Aegean airways or Olympic connecting with Easyjet to Gatwick or Luton, Olympic from Corfu via Athens, or a ferry to Brindisi / Bari and a ryanair flight. Excel and Monarch have Monday flights from Corfu, it may pay to ring them up before you go to Corfu and see if they can do anything for you.