Bestseller: The study guide that helps immigrants pass the citizenship test

It has become the publishing phenomenon of 2007 - and without the usual props of sex or a thrilling plotline.

The bestselling political book of the year is a study guide which helps immigrants to pass the test for British citizenship.

In the week it was revealed that record immigration is fuelling the biggest rise in the population for almost 50 years, Life In The UK has beaten Alastair Campbell's diaries and the latest musings of Boris Johnson to come top of the rankings.

A further five guides to the test, which assesses an applicant's grasp of the English language and knowledge of the nature of British customs, politics and culture, have also made it into the top ten.

According to The Bookseller, the top-selling political title is the official Home Office guide for immigrants, which has shifted more than 80,000 copies this year.

The other books, which combine concise summaries of the information immigrants are expected to know with dozens of practice questions, have collectively added a further 138,000 sales.

By contrast, Campbell's The Blair Years is second in the chart, with 64,000 sales, and Boris's Have I Got Views For You is ninth with just under 21,000 sales.

It means the fast-expanding genre now accounts for almost one-third of the money generated by political books, contributing to a 16 per cent rise in revenues for the sector in the period up to September this year.

Last night, Sir Andrew Green, chairman of immigration pressure group Migration Watch, said the figures demonstrated "yet another - rather unusual - way in which immigration is affecting every corner of our society".

The 24-question exam was introduced in 2005 by the then Home Secretary, David Blunkett, in response to fears that new citizens were failing to integrate properly into British life.

Around 100,000 people take the multiple-choice test every year, with two-thirds achieving the pass of 18 marks out of 24.

Typical questions include, "What is the Grand National?" and "What does Remembrance Day commemorate?"

But there are also some tougher questions, such as: "What percentage of Christians in the UK are Roman Catholic?" (10 per cent) and "What proportion of the UK population have used illegal drugs at one time or another?" (one third).

The Home Office says applicants should not try to pass the test by learning the answers to large numbers of questions - because it selects them from a large, constantly refreshed, pool of possibilities.

But Red Squirrel, the small publishing outfit which produced four of the titles in the top-ten bestellers' list, points out that the pass rates have risen since the guides were first issued two years ago.

Last week the Office for National Statistics (ONS) predicted that by 2031 the population of the UK will have jumped from 60million to more than 70million.

It warns that the ever-increasing levels of immigration will add the equivalent of a city the size of London to the total within the space of a generation.

At least 70 per cent of the population rise would be due to the arrival of foreign citizens, which Whitehall officials said would throw into chaos their planning for essential public services.

Currently, net immigration - the difference between those arriving in the country and those leaving - is running at 240,000.

Three years ago, the Government estimated that the level would be running at 145,000.

The ONS added that if the immigration trend continued, the population of the UK will exceed 85million by 2081.