100 daily attempts to sneak into UK
Immigrants have made around 100 bids a day to illegally enter Britain, official figures have revealed.
Border Force staff and other officials such as the French authorities recorded 11,920 attempts between April and July, according to the Home Office.
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.
Last year the number of so-called clandestines reached 19,003, according to figures released under the Freedom of Information Act.
Lord Green of Deddington, chairman of Migrationwatch, warned that the rise was likely be caused by increased pressure on Britain's borders.
He told The Daily Telegraph: "The sharp rise in the number of clandestines might reflect more effective detection, but an increase on this scale is more likely to be due to increased pressure on our borders.
"Part of that may be due to deteriorating conditions in the Middle East and Africa, but there is little doubt that the freedom of our society, the existence of a black market in labour and the presence of relatives and friends add up to making the UK a very attractive destination.
"The Government is seeking to make it more difficult to live in Britain illegally but it will take some time for recent measures to take effect."
Around 2,500 migrants are camped in Calais, France, wanting to try to travel to the UK.
The Government has already earmarked £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: "We continue to strengthen the security of our borders to stop those who have no right to enter the UK. We have made significant investment 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% 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."
Chief Inspector of Borders John Vine told BBC Radio 4's Today programme: "Clearly the authorities are under tremendous pressure at the border in relation to this issue. Ironically, when I looked at the co-operation between British and French authorities in northern France, I found the people there were actually working very well together.
"There's obviously great pressure on that part of the border. The only thing I can suggest that perhaps is required is more resources.
"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 these people 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."
Mr Vine earlier this week released a report showing that more than 173,000 foreign nationals had overstayed their visas in the UK after 2008.
He told Today: "The Home Office should do much more to try and trace and remove people. The Home Office isn't good enough at removing people from the UK who shouldn't be here."
David Hanson, shadow immigration minister, said: "The Government has ignored repeated warnings from Labour and hauliers about the growing crisis at Calais.
"David Cameron needs to realise how serious this problem is and take urgent steps to work with our allies in Europe to sort it out. Under this Government, illegal immigration is getting worse. That's why Labour has put forward funded plans for 1,000 more border staff to help sort the problems out.
"It is unacceptable that the same people are trying night after night to enter Britain illegally. If they do not have the right to remain in Europe, why are the French authorities taking no steps to remove them?
"We need a European-wide effort to ensure people's immigration status is assessed at the first port they arrive in, as this was agreed as part of the Dublin convention.
"People should not be able to travel across Europe without being apprehended and - if they are asylum seekers - given the support they need. Britain should also be a lead player in the continued efforts to resolve the refugee and humanitarian crisis in north Africa and the Middle East, which is leading to people fleeing.
"Instead of sensible action, the Tories have burned bridges across Europe, which makes it harder to persuade the French authorities and other European governments to act."