Octavia II 1.9 TDI. How do you reduce the tension on alternator belt tensioner to enable you to get a new belt on?

If it's like on the PD130 lump in my car, I was looking at this job in my Haynes manual the other day (in a sort of "I've just paid for someone to do it, I wonder what they did for their hundreds of pounds" kind of way!) IIRC, it's something to do with turning the middle of the tensioner anti-clockwise(?) with a spanner. If no-one's come up with anything better by later on, I'll try to remember to post better instructions...

if it is a PD engine it can be done with the use of a 16 or 17mm spanner put spanner on pulley bolt or square aluminium section on top of the tensioner and pull the spanner towards you