Migrants are looking for new routes to Britain after security at the French end of the Channel Tunnel was stepped up.
France and Britain have jointly increased security at the Eurotunnel terminal in Calais after weeks of disruption to traffic caused by migrants attempting to enter the site to board trains or lorries on their way to Britain.
Traffic through the railway tunnel was disrupted on Friday after a migrant was spotted on a freight train, prompting French border police and security staff to stop the train and search it.
A number of migrants were found on board and returned to French border police who will process them, Eurotunnel said, adding that it had enough capacity to carry all traffic scheduled to travel on Friday.
"The incident shows that now that security at the Eurotunnel site has been increased in line with operating volumes, migrants are seeking new routes to cross to the UK," a spokesman for the tunnel operator said.
The freight train was sent back to a yard operated by SNCF, the French national railways, at Frethun, near Calais. Eurotunnel said it had already requested that security be increased at the yard in line with measures in place at its own site.
Authorities have been watching for signs of migrants seeking new routes to Britain as a result of the crackdown in Calais.
Belgian police said they had not seen significant signs of migrant activity at Belgian ports, but officials said a three-way meeting on the issue with their British and Dutch counterparts was expected to take place in about a month.
A British embassy official in Brussels confirmed discussions on the issue were already taking place with the Belgians.
