Illegal UK entry arrests surpass 27,000 in three years
More than 27,000 people suspected of illegally entering the UK have been arrested over the past three years, figures obtained by the BBC show.
The statistics from 39 police forces in England, Wales and Northern Ireland showed nearly a 25% rise in arrests from 2013 to 2015.
Many of those arrested were found at motorway service stations and truck stops, having hidden in lorries.
The Home Office said it wanted "long-term solutions" to illegal migration.
Four forces - including Police Scotland - did not provide data, while some only provided partial information.
Commons Home Affairs Committee chairman Keith Vaz called for "urgent action" to tackle the problem, while former Special Branch ports officer Chris Hobbs called the figures "appalling".
BBC home affairs correspondent Danny Shaw said the figures were the most comprehensive yet to be compiled, and highlighted the increasing burden placed on police by migrants who have slipped through border controls.
The figures, released under the Freedom of Information (FOI) Act, show officers made 7,709 arrests for illegal entry in 2013.
The number increased slightly to 7,913 the following year and rose to 9,600 in 2015, when many countries in Europe were struggling to deal with the refugee crisis.
The total over the period from January 2013 to April this year was 27,800.
This does not include people arrested for staying longer in the country than their visa entitled them to, nor those detained at ports and airports, who are dealt with by Border Force staff.
Meanwhile, a separate FOI request showed that across the Channel, officials at ports in France, Belgium and the Netherlands intercepted 145,157 would-be migrants to the UK from 2013 to the end of March 2016.
By BBC home affairs correspondent Danny Shaw
If you want to find figures on legal immigration, the Office for National Statistics has plenty. Illegal immigration is a different matter.
Clandestine migrants don't want to be found, let alone counted for statistical purposes.
Besides, the government wouldn't be keen to advertise how many people are in the country who shouldn't be.
But the police arrest figures provide a good indicator of the scale of the problem.
Of course the numbers don't include illegal entrants who've managed to stay under the radar.
But they do highlight the increasing burden on police presented by those who've slipped through border controls unnoticed.
Mr Hobbs said: "Obviously these people are still getting through.
"And these are the ones that are being detected by police. What about the ones who are getting through undetected, who simply disappear?"
"The figures really are unacceptably high. We are an island and really we're not making full advantage of the fact that we are surrounded by sea. We should be doing far better, and the figures are appalling."
Mr Vaz told the BBC the "astonishing" figures "basically show[ed] that our border is not secure".
"The government keeps maintaining that they have got water-tight security at our borders," he said.
"If 27,000 people have been arrested for entering the country illegally by our police forces, then it shows that this problem is even worse than we had anticipated and we expect urgent action to be taken."
Mr Vaz said the problem meant "greater pressure" on the UK's police forces, as they were "having to do the work of border security". More resources were needed, he added.
Dover's Conservative MP Charlie Elphicke has called for further patrols in the Channel.
He said: "We need to not just dismantle the Jungle at Calais.
"We need to deal with the camps at Dunkirk and elsewhere and by the Channel ports. We also need to deal with the problem of people-trafficking by small craft.
"That's why I've been calling for a marine-led new Dover patrol to make sure that the English Channel is kept safe and secure."
The Home Office said where someone is found to have no right to remain in the UK, it will take action to remove them.
"As part of the ongoing action we are taking to secure our borders, we have invested tens of millions of pounds to bolster security at ports in northern France," a spokesman said.
"We are also committed to finding long-term solutions to the problem of illegal migration, which is why we created the Organised Immigration Crime Taskforce last year to work with law enforcement and international partners to target the organised crime gangs behind people smuggling."
There were "clear signs" that the action was working, he added.