Having found someone locally in the classic back street who specialises
in belt drives etc. I think I am possibly going to have to eat some
humble pie !! Having seen plenty of machines with multiple belts and
looked up V belt drive design and found that for the size of pulley
(50mm OD) I have the recommended maximum power was 1 kW, then my
thinking was a 75mm pulley and double it up.

The problem I have was that the driven pulley was regularly coming
slack plus the power at the saw blade was not really matching the power
of the motor and there was a lot of heat in the driven pulley. Anyway
I've to give all the data to this local guy and see what he comes up
with - and it may well be something that has been mentioned here, and
....ummm... oops....it could well be that his solution is different from
what I was thinking !!

Rob