Latest communication from my brother says:

"The throttle cable is fine, but the pump throttle arm felt a little
tight / gritty (without cable attached)

Air filter isnt that old, but surely doesn't cause that all of a
sudden, Oil level - again has used some but not massively or more than
normal, Pulled fine before taking it to them eitherway without smoke.

More than a bit clackety - sounds like my valves are sat on the
pistons!

Will check vacuum hoses - nothing looked out of place, although a
breather hose has split but has been a little for a while with no
problems. (special part taper hose)"
Thanks for the thoughts so far.
James