Dave, thanks. I looked at Think's web site and its not clear exactly what fitting it might be but if its what I think it could be then circa £70 seems steep!
Bozz, i'm not convinced it is necessary but if it was a cheap item I might have had a go. I guess the alternative is always to crank the engine over while the immobiliser is on before properly firing it. I dont think I could be bothered each time on routine running to do that though, only after a week or twos lay up.
I'm not expecting premature wear anyway so will probably leave things as they are
Paul