Authorities are believed to have arrested a person who was found inside the Channel Tunnel.
A Eurotunnel spokesperson said a “criminal procedure” has followed the discovery of someone inside the tunnel.
It is not know have far the person had managed to get before being discovered by the French authorities, who are now handling the matter.
A spokesperson for the Channel Tunnel operator said: “Eurotunnel can confirm that a person was detected inside the Channel Tunnel.”
They said the person had been taken into custody by the French authorities.
The Eurotunnel spokesperson added: “As there is now a criminal procedure in place we are unable to comment further at this time.”
Reports have suggested the intruder was a man who may have set off on his journey last Monday.
The incident happened shortly after the Eurotunnel closed the tunnel after a “large and co-ordinated” group stormed the track at Calais.
A couple of months before that, a man was arrested after being found near the exit in Folkestone in Kent.
Additional reporting by Press Association