That's where you're making a big mistake. A tariff is indeed a tax imposed on goods coming from another country. However, VAT is "merely" a tax, not a tariff, as it is imposed on ALL goods on sale in the UK (except those exempt, like childrens clothing and food staples among others) IRRESPECTIVE OF WHETHER THOSE GOODS WERE IMPORTED OR MADE IN BRITAIN. There is no distinction, nor any disadvantage to any other country over our home grown goods.
However, there can be an import duty (excise tax) which is entirely separate from VAT. If I buy dietary supplements from the States, I have to pay an extra duty on them when they arrive here. Nothing to do with VAT. That's the tax you should be complaining about, and I'd join you.