Andy,

I have re-thought the workshop loading and done
some cable calcs and put them on...

http://www.gillandroy.com/diy/workshop/electrics

It looks like a 16mm T&E with 6mm CPC will
satisfy the regs with whatever protection is back at
the house. However, I think I will put in a separate
10mm CPC (belt & braces) and have a fused
switched by the house CU as you suggested.

I'm not clear about the sort of Fuse to use ?
BS 88, BS1361 ? Or what? Or will that get
determined by the switch-fuse unit.

Do I take it this is the sort of thing you are suggesting...

http://www.tlc-direct.co.uk/Products/WY108.html

Many thanks for your help,
Roy