Martin,
Sorry for the delay in replying, you're correct about moving the tensioner by the nut in the centre of the roller, it was very stiff but no match for brute strength and ignorance
After examining the roller I found a couple of chips, see photo, so I decided to play safe and get the new tensioner anyway, the car has done 99k anyway.
The new roller was fitted with the pin in place and then removed from above, by my ever helpful assistant (dad)
after tension released from below. New belt fitted, I looped over new crank pulley and tensioner first but not the pulley at bottom then moved tensioner roller with spanner and looped over that as it has no flange unlike the bottom roller. Runs like a dream, new bulb and front wipers and went through MOT first time.
Thanks for all help offered, until next time.
Stuart