I do hope you get it sorted soon, must be so frustrating having a seat stop it from being used. I'd definately take someone up on the offer of a seat pick up from France, they have loads over there. Or just pay a breakers to send one over, will be a bit of cost but worth it in the long run. I've had parts send over from France before without issue.
Also if you have it booked in for an MOT you can even legally drive it there without one, so long as its being driven straight to the MOT station:
"You cannot drive or park your vehicle on the road if the MOT has run out. You can be prosecuted if caught. The only exceptions are to drive it: to or from somewhere to be repaired."