Multiple Zones made up of UK Postcode Areas and CountriesBrowser Info Environment
BAND 3 - £100 + Vat – Northern Scotland, Northern & Southern Ireland, Isle of Wight,
Northern Ireland, Southern Ireland, Isle of Wight (PO30-41), Northern Scotland - DD, PH1-14, AB10-30,32,39, AB(exc10-30,32,39), IV(exc41-49,51,55-56), KW1-14, PH15+
BAND 4 - £160 + Vat – Scottish Highlands & Islands, Isle of Man, Guernsey & Jersey
PA20-38, IV41-49,51,55-56, KA27-28, PA41+, KW15-17, GY (exc 9)
1. The first country to match a rule
2. The last state/city etc rule match within a country rule (or none)
You can have more than one address match rule to match a zone. Some locations could be countries or counties, depending on how you have the countries and counties/states lists set up (not part of ZBS, but if you dont want to edit overrides by hand, see my Country State Manager addon)
So, for the majority of the UK, your Band 1, you can make a country match to the UK your default
Country equals Isle of Man|Guernsey|Jersey => Band 4 // cross off the easy ones
Country contains Ireland|Eire|Republic of Ireland => Band 3
Country equals United Kingdom|UK|England|Scotland|Wales etc. => Band 1 // domestic default
Postal Code begins with PO30|PO31|PO32|PO40|PO41 etc. |DD|PH1|PH2 etc. |AB1|AB2|AB3 etc. => Band 3
County equals Isle of Wight => Band 3
County equals Isle of Man|Guernsey|Jersey => Band 4
Postal Code begins with PA20|PA21|PA30|PA31 etc. |IV41|IV42|IV43 etc. |KA27|KA28| => Band 4
The above is a long way from complete, I have left out some details but hopefully it gives the right idea.
If you know how to do regular expressions, you may be able to use some regular expressions to simplify the bigger postcode ranges. However, unless you really know what you are doing with regular expressions, something like the above is more maintainable.
The attached file is a subset of the rules a ZBS user has built for UK shipping. His requirements are obviously different to yours and he has highly customised countries and states/provinces lits, but maybe they could help get you started.