Border Force staff are struggling to cope with queues to check passports at Heathrow Airport, it has been claimed.
Personnel are said to have been redeployed from Channel ports to help airport colleagues deal with delays.
An unnamed member of south-east Border Force staff told the BBC: "We are being crucified. There is a high percentage of long-term sick due to stress.
"We are being pushed completely and we cannot cope."
The whistle-blower reportedly said staff were not given sufficient time to examine passports properly.
He claimed some Border Force staff had to start their shift at Dover, drive to Heathrow to do three hours' airport work, then drive back, according to the BBC.
Figures show targets for how long it takes to clear immigration were missed for some passengers at the airport in west London last month.
An aim for Border Force to process 95% of those from outside the European Economic Area within 45 minutes was not met in the four terminals in June.
The proportions cleared within the target time were 89.4%, 91.3%, 93.3% and 94.1% in terminals two, three, four and five respectively.
Keith Vaz, chairman of the Home Affairs committee, said: "During the peak summer months there is always an increase in passenger numbers.
"It is a no-brainer for those who run Border Force to have made contingency plans to increase staffing levels for this period.
"Rather than deploying officers from policing border security issues additional staff should have been drafted in to deal with passport checks at Heathrow."
Why are you making commenting on The Herald only available to subscribers?
It should have been a safe space for informed debate, somewhere for readers to discuss issues around the biggest stories of the day, but all too often the below the line comments on most websites have become bogged down by off-topic discussions and abuse.
heraldscotland.com is tackling this problem by allowing only subscribers to comment.
We are doing this to improve the experience for our loyal readers and we believe it will reduce the ability of trolls and troublemakers, who occasionally find their way onto our site, to abuse our journalists and readers. We also hope it will help the comments section fulfil its promise as a part of Scotland's conversation with itself.
We are lucky at The Herald. We are read by an informed, educated readership who can add their knowledge and insights to our stories.
That is invaluable.
We are making the subscriber-only change to support our valued readers, who tell us they don't want the site cluttered up with irrelevant comments, untruths and abuse.
In the past, the journalist’s job was to collect and distribute information to the audience. Technology means that readers can shape a discussion. We look forward to hearing from you on heraldscotland.com
Comments & Moderation
Readers’ comments: You are personally liable for the content of any comments you upload to this website, so please act responsibly. We do not pre-moderate or monitor readers’ comments appearing on our websites, but we do post-moderate in response to complaints we receive or otherwise when a potential problem comes to our attention. You can make a complaint by using the ‘report this post’ link . We may then apply our discretion under the user terms to amend or delete comments.
Post moderation is undertaken full-time 9am-6pm on weekdays, and on a part-time basis outwith those hours.
Read the rules here