So - managed to successfully change the solenoid out. Removed a nice section of trim inside the boot, but in hindsight, it could probably be done without doing that. Most difficult piece is getting the fuel cap surround detached from the body panel - it's held in place with the clips shown in the pics - but can be wedged away from the bodywork with extreme care (not to chip paintwork) as some force is needed. About an hour to complete and replacement part was £20 on amazon. Thanks for the advice @Stevey Y.
