May need to cancel a flight. I have a dilemma what to do. Where should I start?

TELLIT01

It may only be a small charge to change ticket date but you may also be hit for more money if the new ticket is more expensive than the one already purchased.

Alfrescodave

As you are very likely to loose several hundred pounds on cancelling your plane tickets; can you still go and offer this amount to your friends as payment for their hospitality etc. Obviously it does depend upon your relationship but it could be seen as them actually saving you money.
A tricky conversation that requires utmost diplomancy.