so I will have to up the budget by £13 and buy a battery powered digital
stat
/if/ the boiler is compatible with such a device ?

The boiler will be compatible with a battery powered digital stat.

thanks for your continuing input, how about the cable run in relation to
the regs ?

Either:

(a) claim you know nothing about it
(b) get it signed off at great expense by an electrician
(c) get it signed off at great expense by the local council
(d) use an RF stat

With it buried in plaster, I doubt you'd be able to claim it wasn't fixed
wiring, despite the fact that the whole lot sits off an FCU/plug+socket. You
could always ask your local BCO for their opinion.

Christian.