It is believed that the authorities arrested a person who was found in the Channel Tunnel.
A Eurotunnel spokesman said a “criminal case” was due to the discovery of a person in the tunnel.
It is not known how far the person has come before being discovered by the French authorities now dealing with the matter.
A spokesman for the Channel Tunnel operator said: “Eurotunnel can confirm that a person was discovered in the Channel Tunnel.”
They said the person was taken into custody by the French authorities.
The Eurotunnel spokesman added: “As there is currently a criminal case we cannot make any further comments at the moment.”
The intruder was reportedly a man who may have set off last Monday.
The incident occurred shortly after the Eurotunnel closed the tunnel after a “large and coordinated” group stormed the route in Calais.
A man was arrested a few months earlier after being found near the exit in Folkestone, Kent.
Additional coverage by the Press Association