Illegal immigrants may be exploiting staff shortages at southern England's sea ports, a report has suggested.
Border Force managers at Dover, Poole, Portsmouth and Southampton said they were understaffed in 2017/18, the Independent Chief Inspector of Borders and Immigration found.
The inspector, David Bolt, said some of the managers had said the force was "resourced to fail".
The Home Office said it had accepted some of the report's recommendations.
Border Force had made prevention of "clandestine entry" to the UK a "very high" priority, the report said.
But it said Border Force officers claimed there were "not enough of them to meet increasing operational pressures".
A group at one port commented: "The border is not secured by any stretch of the imagination."
Inspectors found that the boots and back seats of tourist vehicles were not routinely inspected.
In Poole and Portsmouth, the discovery of a clandestine entrant would normally lead to all other detection work being suspended, the report said.
Officers in Portsmouth told inspectors migrants exploited the port's "limited resources" by splitting up and hiding in different trailers.
No lorry driver or operator had been fined for carrying migrants to the UK since July 2016, inspectors found.
The penalty system was "broken" and should be fixed, Mr Bolt urged.
In March, the four ports - together with Newhaven and Plymouth - were 54 staff short of an agreed creation of 488 posts, the report found.
A total of 882 illegal immigrants were detected at the ports in 2017/18, compared to 1,119 the previous year.
In a statement, the Home Office said it was pleased at the decrease in clandestine arrival numbers.
It added: "However, we accept that improvements can be made and will be taking forward the recommendations."