Hi Tony, sorry for not replying sooner but only just seen your posting.
I used the cam locking tools, to check the timing in the first place.
Then remove the throttle body and then you will gain access to the tensioner.
I also found this useful info to gauge the amount of chain stretch using the BMW-Mini mechanical tensioner, if the measurement is 68mm or below then new tensioner will do it. If it's over 68mm then chain is due for replacement.
On a new chain it's around 54mm.



This website is also useful

http://www.promini.com/technical/engine/files/MINI-Cooper-R56-Engine-Rattle.php

Martin.