Britain has issued two million passports to immigrants since 2000 - one every 150 seconds, a media report said.
Last year alone, a record 204,541 requests for a British passport were approved by the government, the Daily Mail reported citing the British home department.
The main beneficiaries of British citizenship were from India, Pakistan, Nigeria, China and the Philippines.
The total number of passports given out since then stands at 2,053,396, the report said.
This means one migrant being granted British citizenship every two-and-a-half minutes.
Once approved, new citizens were treated in the same way as anybody else with a British passport. They get access to benefits such as housing and jobs.
In Britain, a person qualifies for citizenship after living and working in the country for five years and if they were not engaged in any criminal activities.
However, critics insisted that the government have adopted a deliberate policy of mass immigration for political reasons.