I'm in the US, so you'll have to forgive my ignorance, here, but isn't the UK's tax law pretty tightly unified at the federal level? I once got into an argument with the county (Travis, Texas) over how to account for a penny difference in the calculation of sales tax. The resulting form involved (like) 6 govt entities and 7 pages of calculations.

EDIT: if I'd been in Burnet, it'd be almost completely different forms & calculations.