General Rules of Thumb...
Shipping items which are VAT-exempt i.e. zero sales tax. If so, then the shipping costs are also taxed at 0%.
Shipping items at the reduced 5% VAT rate i.e. 5 percent sales tax. If so, then the shipping costs are also taxed at 5%.
Shipping items at the standard 20% VAT rate i.e. 20 percent sales tax. If so, then the shipping costs are also taxed at 20%.
Shipping costs (and any other costs such as packaging, admin or sundries) should come before you calculate VAT on your Invoice. See the example below – the Sales Tax is added right before the Total Sum/balance.