with the tensioner, you have to take out the driver headlight, indicator, i took the bonnet off too.
then you slcken off the tensioner wheel (dont turn it more than once) aniticlockwise with a 7mm allen key .
then with a 22mm open ended spanner turn the nut on the wheel anticlockwise not clockwise like it says in the haynes manual, then when there is like 2mm of freedom on the belt tighten up the allen key.
helps if you have small hands like me cos theres not much space in there, also wear a plastic glove its as grimy as you like.