Fears that illegal migrants are finding a new route to Britain have been borne out by new figures yesterday.
Officials said 1,251 had been caught trying to board ferries from Bilbao in northern Spain to Portsmouth in the first eight months of this year.
That compares to 436 in the whole of 2016.
Brittany Ferries, which runs the ferry route, has called on port security in Spain to be tightened to stop offenders repeatedly trying to board ships.
Brittany Ferries, which runs the ferry route, has called on port security in Spain to be tightened to stop offenders repeatedly trying to board ships
A company spokesman said most of those involved are young, male Albanians who are ‘well-organised’ and repeatedly target the port’s perimeter in Bilbao.
An increasing number of migrants are taking the short route from northern Africa to southern Spain and then working their way north. Others are avoiding northern French ports as security is harder there.
Portsmouth City Council is looking after more than 40 asylum-seeking teenage boys who arrived unaccompanied.
There are two Brittany sailings each way each week between Portsmouth and Bilbao and the company also runs freight services between Bilbao and Poole.
Brittany Ferries revealed 99 detentions have also been made in Bilbao, Portsmouth or Poole, in the first two weeks of this month.
The spokesman added: ‘Bilbao remains an attractive target for criminal gangs.
‘In neighbouring Santander, those who repeatedly target port facilities are sent to a detention centre near Madrid before being deported.
‘In Bilbao, a port infraction is treated as a civil misdemeanour and offenders are simply released to try again.’
According to Brittany Ferries, most offenders try to get into a sealed container or trailer before it boards a ship, rather than trying to get on to a ferry indirectly.
People may target routes into Bilbao where drivers stop and they then try to jump into the back.
Curtain-sided vehicles – with tarpaulin sides – are easier to get into and people can slash the covers with a knife to get inside.
The Road Haulage Association has previously advised members not to stop too close to ferry ports in France and Spain.
Officials said 1,251 had been caught trying to board ferries from Bilbao in northern Spain to Portsmouth (pictured) in the first eight months of this year
If stowaways are discovered upon arrival in the UK, gas detectors are usually used to identify high levels of carbon dioxide inside a trailer, indicating that there may be a person inside.
Last month Spanish newspaper El Pais reported that a major factor in the increase in detainments was the dismantling of the so-called ‘Calais Jungle’, where many foreign nationals had set up camp.
A Home Office spokesman said: ‘Working with our law enforcement partners at home and abroad we use intelligence to keep our borders secure.
‘We have also invested in new detection technology and are working with port operators to improve the controlling, screening and processing of unauthorised arrivals.’
Portsmouth City Council leader Councillor Donna Jones said: ‘We are very grateful for the efforts made by Brittany Ferries and Border Force to tighten security around ports to ensure people are not entering the UK illegally.
‘The council has the responsibility to look after unaccompanied asylum-seeking children so any entering the country illegally, without a genuine need for asylum, place an additional burden on our already limited financial resource.’