Post-Brexit controls on food, plant and animal imports to Britain from the EU have come into force.
Health certificates will now be required on EU goods ranging from cut flowers, to fresh produce including meat, fruit and vegetables.
Some industry bodies raised concerns the rules could cause delays and push up costs, but others said they would help UK farmers be more competitive.
The government said its border model would "minimise burdens for traders".
The UK left the EU exactly four years ago, but it has taken some time for the government to implement new trade rules - legally required under the Brexit agreement - for goods travelling from the EU to the UK.
Wednesday marks the start of the changes as Britain begins reversing the free flow of such goods, which has been allowed since the creation of the EU single market in 1993. Red tape has already applied for British exporters trading in the other direction for three years.
The implementation of the changes has been delayed five times, in part to give businesses time to prepare and to reduce disruption to supply chains. The new border checks will also be phased in over the next year, with physical checks starting from 30 April.
Read more on BBC news.