Updated: The customs policy email address in section 3 has been updated.

From 1 May 2016 onwards, you should make out a transit declaration for all non-UK consignments of household effects, personal property and private vehicles for immediate onward delivery to the member state after arrival into UK.

Alternatively, these consignments can be customs cleared to free circulation upon arrival into the UK with the proper payment of all import duties and other charges liable. The owner of that consignment may then apply retrospectively for ToR relief from the customs authority of the member state where they then set up their new residence. However, there is no guarantee that the relief will be awarded and UK customs will not be able to influence the decisions made by the host customs authority.

https://www.gov.uk/government/publications/customs-information-paper-32-2016-tor-consignments-uk-clearance-approved-depositories-and-transit-to-eu