Workbooks is pre-set with a list of Tax Regimes. These are political/administrative territories which have their own tax raising powers.
Various tax tables and rules will be stored against each tax regime, including your Sales Tax codes and rates (VAT). The contents of this area will depend on which Workbooks Edition you've subscribed to.
The list of regimes is intended to be comprehensive but if the one you require is not available please contact Workbooks Support. NOTE: The code for the UK Tax Regime is GB and the description is United Kingdom.
To view / change Tax Regimes, click Start > Configuration > Accounting > Sales Tax Regimes.