Thanks for that - I have been back and forth from the tool shop on the pushy three times now - each time I come to a new/different size allen key.
The balancer needs 6mm - and the belt adjustment for aircon needs 8mm.
The only problem I have now is slackening the power-steering - which is, to put it very mildly, a bastard (especially as I don't have a manual - haven't been able to track one down).
Can you remember which bolts do what, in sequence, to loosen the power steering unit/belt adjustment?
I have loosened the bottom right pivot bolt, but there is a hex bolt to its left, which should slide the unit back and forth (has teeth) in order to tighten/slacken - it simply will not budge.