I take it from the pic which Ian kindly posted, that item 7 is the idler which I will remove when removing the compressor. Is item 5 the tensioner and should I replace that at the same time? How easy is it to replace the belt/tensioner? Access looks a bit limited.
You dont need to replace the tensioner, unless its old and noisy. Access is poor, you need a 15mm swan neck spanner to remove the tensioner and/or idler, and also to slacken the tensioner to remove the belt.
Ians top tip (from someone here) for unloading the tension on the belt to remove or refit the belt, is to tie some rope to the ring on the other end of the spanner, get the spanner on the tensioner nut, feed the rope up into the engine bay, then heave ho and tie it off on the dogbone engine mount, you can then remove the belt easily. Just be aware of the rope slipping or the spanner coming off the nut.