There are special customs requirements for commercial goods or samples which are imported or exported by passengers in their accompanied baggage (hand carried) or in a small motor vehicle (carrying less than 9 passengers and weight 3.5 tonnes or less). This is known as Merchandise In Baggage or MIB.
MIB goods include the following:
whether or not they are:
HMRC has announced how these rules will be applied in the EU if we have a no-deal Brexit. This will include the introduction of transitional simplified procedures for the import or export of goods valued at below £900 and weighing less than 1,000kg. This simplification will not apply to licensed, controlled, or excise goods. For all other goods a full declaration will be required before the goods enter or leave the UK.