Migrants made up to 100 bids a day to illegally enter the UK during summer, officials figures from the Home Office have shown.
Their data reveals Border Force staff and French officials recorded 11,920 attempts to enter Britain between April and July.
Its records show a steep increase in the number of times illegal immigrants were detected trying to make it into the country since the coalition took power in 2010, when just 10,916 were identified over the financial year.
This 11,920 figure suggests at least 100 attempts to enter the UK each day were made in the summer – although this does not mean 100 people are trying to enter each day. Migrants may have made multiple attempts during one day.
The figures, released under a Freedom of Information request from campaign group Migration Watch, also showed the number of so-called clandestines reached 19,003 last year.
French authorities said about 2,500 migrants are camped in Calais, France, wanting to try to travel to the UK.
The UK’s chief inspector of borders, John Vine, said more resources were needed to deal with security at French ports.
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He told the BBC Radio 4 Today programme: “We found that people found in lorries were being released to the French authorities but no record was being kept of who they were.
“And of course when they try again and very often succeed in getting into the UK as irregular migrants, the authorities in Britain have no record of who they are.”
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The Government has already set aside £12m to improve security and has urged lorry drivers and tourists to take extra precautions to stop would-be migrants boarding their vehicles.
Immigration and security minister James Brokenshire said it is continuing to strengthen the security of Britain’s borders, “to stop those who have no right to enter the UK”.
He said “significant investments” had been made in ports in Northern France to improve security and infrastructure.
“Using some of the best technology in the world, our officers prevented more than 18,000 attempts to cross the Channel illegally in the year to April 2014 – a rise of more than 60 per cent on the previous year.
“We have also committed £12 million to further bolstering security at Calais and driven down the cost of back-office functions, allowing us to invest more in front-line operations.”