Having the customary headache that seems to accompany shipping setup and desperately need some advice to point me in the right direction.

I have 3 types of product for which a category has created for each.
Each product is to have 2 shipping options - standard and next day(zone based)
Charges are zone dependent and as such I have created the following regions for the UK, each with the indicated service available.

England, Wales & Scottish Lowlands
Standard
Next Day
Scottish Highlands
Standard
Next Day
Northern Ireland
Standard
Next Day
Channel Islands
Standard
Isle of Man
Standard
Scilly Isles
Standard
Collection from shop

I have it all working except the item marked in red.
As mentioned previously there are 3 types of product, A, B and C.
For the England, Wales & Scottish Lowlands zone Type B and C always carry a delivery charge, for Type A delivery becomes free over £100. Is there anyway to make delivery free over this limit, for this category, in this zone? Is there another way to structure this delivery schedule that this would work?

Dave