The Home Office says 11,920 entry attempts were detected at Calais and British ports in the first four months of this year alone – equivalent to almost 100 a day.
Migration experts said that Britain is one of the most "attractive" destinations for migrants in the World and suggested that many more illegal immigrants are likely to have successfully made it into Britain.
Lord Green of Deddington, the chairman of Migrationwatch, said:
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 are seeking to make it more difficult to live in Britain illegally but it will take some time for recent measures to take effect.In 2011/12 migrants were caught trying to enter Britain a total of 9,632 times, a figure which by last year had almost doubled reaching 19,003. This year the number has risen sharply, and at current rates could exceed more than 35,000 by the end of the year.
Experts said that migrants were attracted by Britain's unregulated labour market, the ability to get free health care on the NHS and relatively generous welfare system.
Once immigrants from African countries have made their way into Europe, they can travel across borders without needing to show passports or identity cards to France. In Calais more than 2,500 migrants, mainly from African countries such as Eritrea, are camped around the town. Many are prepared to risk their lives in an attempt to enter Britain.
The Home Office say they 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.
But if the pressure of illegal migration is so strong, there's something wrong with the incentives. The UK is specially attractive. The only way to stem the flow is to make the UK less attractive to immigration.