When you order goods online you don’t expect to pay any additional taxes when they are delivered. This is currently the case for goods ordered from a supplier in the UK or the EU.
However, if you order goods from outside the EU you may receive a notice saying you must pay the import VAT before the goods can be delivered. If the supplier has already charged you the import VAT, you should not have to pay it twice.
If the UK leaves the EU without other arrangements in place (no-deal Brexit), import VAT will be due on all parcels of goods worth no more than £135, which arrive in the UK from the EU or from other countries. If the parcel is a gift to the recipient no import VAT is payable, but the parcel must be clearly marked as a gift from an individual to another individual and must be intended for personal use.
The business which sends the parcel to the customer in the UK should register with HMRC and pay the import VAT, or arrange for the parcel operator to pay the VAT. The registration is required even if the goods are zero-rated for VAT.
If your business relies on goods sent as small parcels through the post, be aware of this change in the rules. If you are sending small parcels to non-business customers in other EU countries you may have to pay import VAT to those countries.