Vehicles passing through major ports and the Channel Tunnel are to be screened for radioactive material in a bid to combat "nuclear terrorism".
Channel Tunnel traffic is to be screened for nuclear material
The plan was within a Franco-British communiqué after French President Nicolas Sarkozy held talks with Prime Minister Gordon Brown in London.
A Home Office spokesman said the intention was to screen all major points of entry to the UK from France.
But the Channel Tunnel is singled out for special mention in the document.
It says: "We will work together to combat nuclear terrorism by screening traffic including that passing through the Channel Tunnel."
A Home Office spokesman said the "intention is to screen traffic at all major points of entry" for "any radiological material that could be used for terrorist purposes".
He added: "It is about making sure dangerous substances and materials are not getting into the country."
He said "limited" nuclear screening was already taking place at some major ports.
When an alarm is triggered, Customs officers will be able to ask police or "radiation advisers" to intervene, he added, with procedures in place to ensure the "safe removal and disposal" of any radioactive material.
The prime minister's official spokesman said the move was not in response to any specific threat - but was the kind of issue on which the British and French governments would be expected to collaborate.
The 36-page communiqué sets out key areas where Britain and France plan to work more closely together.
It goes into particular detail about defence and security, pledging greater co-operation on threat analysis, technical and operational matters.
The screening of radiological material inside vehicles entering the UK has been conducted at major UK sea ports and airports since 2004.