India is among the top five countries named as the hub of illegal migration to the UK.
Nigeria, Pakistan, China, and Bangladesh are the other countries named by the UK Home Office as the hub of illegal migration, according to a report in the Daily Mail.
It claims that a latest Home Office study reveals a "robust estimate" of 863,000 illegal migrants living in the UK, 70% of whom are believed to be based in London.
Their origins have been deduced based on the nationalities of people detected by the authorities.
Britain's Immigration Minister Mark Harper blamed the problem on "uncontrolled immigration" over the years under the Labour government and stressed the Tory-led coalition was determined to get "tough on illegal immigration".
The latest figures come from the London School of Economics and are included in a study titled 'Practical Measures for Reducing Irregular Migration.'
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The analysis also reveals that around 10,000 foreigners who had no legal right to live in Britain have been granted permission to stay under a provision that allows a migrant who has lived in the UK for 14 years the right to abode.
The British government has come under repeated attack for failing to get a grip on Britain's mounting backlog of immigration cases.
Recently, it was reported that Capita, a company awarded a contract by the UK Border Agency (UKBA) worth up to 40 million pounds to track down more than 174,000 immigrants who may be living illegally in Britain, may have been wrongly pursuing people who have the right to stay in the UK and others who left long ago.
The UK's immigration problems are also set to multiply as Bulgarians and Romanians will gain the unrestricted right to live and work in Britain from December 2013, when temporary curbs imposed in 2005 to protect the British labour market within the European Union expire.
Prime Minister David Cameron has insisted the country will demand new restrictions to keep out benefit tourists as it fears a tidal wave of EU immigrants from next year.