Do it now, before its growing strongly - but keep a good rootball around it and try not to break any roots, water in well in new position, make sure the new hole is large enough and deep enough to accommodate the whole thing without bending any roots.

Thanks Bamboo, you're a star - I will get to it this afternoon

For some reason I always thought Penstemon was a bit more tender than Delphiniums, Phlox etc and couldnt be moved

Moving things is always possible, unless they're very mature - the trick, though, is to deceive the plant into not realising, so if you've heavy, damp soil, it's much easier - it sticks in a solid lump round the roots. Not so easy in light, dry sandy soil.

Its moved - though I have to say how surprised I was at how shallow it was...

Well, its only a perennial, not a shrub.

True. Also given all Ive done the last couple of days has been taking out hebe and an apple tree, maybe I was overestimating the task.

LOL, sure is a difference between an apple tree and a perennial...

just incase you lose it take a load of cuttings,they will grow really quick,and easy to take.