Bit of an update, I bought some spring compressors, compressed the spring and tried to refit the seat.

As predicted it didnt want to stay .... looked back here for more advice and see that you think the spring has broken... I think you are right as the end is very sharp.

The car is a 2002 52 plate with 101k miles on the clock, well out of any sort of warrenty or recall I should think.

As I dont intend keeping the car for more then another 5-6 months I have bought a second hand strut off ebay for