Friends of ours had a 2 week holiday booked a couple of years ago with TUI. Cant remember the reason why but they cancelled and rebooked a city break which only cost them slightly more than the deposit they had originally paid.. so that is another option they may well let you do.
yes single trip insurance does cover for cancellation from the moment it is taken out. If you think back to what feels like many moons ago now.. back in the dark days before t'internet it was standard practice for the travel agent to sell us the single trip insurance with our booking. It was only ever single trip and protecting us against cancellation was one of their selling points. Sometimes we managed to get lucky and have it thrown in for Free
![:D](/storage/forum/smilies/vgrin.gif)