From 28 March 2019, it is mandatory for certain trailers taken out of the UK to be registered with the DVLA (Driver and Vehicle Licensing Agency).
Trailers with a gross weight of over 750kg used for commercial purposes, and those with a gross weight over 3,500kg which are used towed by private vehicles, must be registered and have the registration documents with the vehicle towing them.
The change is a long awaited compliance by the UK with the requirements of the UN 1968 Vienna Convention on Road Traffic, which the UK has ratified. Although much of the UK´s traffic law already complies with the convention, the registration of trailers is one element which was outstanding. This will come into force on 28 March 2019.
In order to comply with the agreement, trailers that are used internationally in countries also covered by the convention must be registered, if they fall into the required categories. A full list of countries is available, along with more information, on the UK government website gov.uk/guidance/trailer-registration, where you will see that you do not need to register trailers used in Spain, but you must register if you drive through France, and other countries, if you travel between the UK and Spain.
In order to try to make the process easier, and because there is expected to be a large number of trailers that fall into the categories, the DVLA has launched a new website, where the information on the trailer can be submitted, before the registration certificate is sent to you through the post, and an email confirmation, which will allow you to then have the number plate made which must be displayed on the trailer.
You can register your trailer, and find out more, here: gov.uk/register-trailer-to-take-abroad