Britain’s border guards can no long use X-rays to examine lorries they believe may contain illegal immigrants while exiting French ports, it has been claimed.

Lucy Moreton from the Immigration Services Union said French authorities had banned the devices, which take around an hour to scan each vehicle, on health and safety grounds.

She said: The French will not allow us to use them for looking for illegals. They only allow us to use scanners to search for contraband, not people.’

Checks at border crossings have been stepped up following the terror attacks in Belgium, with freight in and out of the country severely delayed as a result.