Nearly half the Keighley members of the British National Party have left the organisation since the end of 2007, according to information leaked on the Internet.

It is the second list to reveal the names of BNP members in a year, with this one, released on Wikileaks, claiming to be taken from April 2009 records.

The information, which has been analysed by the Guardian newspaper, shows that the BNP has 11,811 members, including doctors and military personnel, and has benefited from a surge in female recruits — with one in eight women now signed up as members. While support for the party has grown in Leicester, Lancashire, Derbyshire and Lincolnshire, overall it has reduced in Bradford and significantly so in Keighley.

In a comparison of the leaked figures from last autumn’s list of names from the end of 2007 to the latest list, BNP membership in Keighley has shrunk from 52 to 29 people, overall a decrease of around 44 per cent.

It is the highest decrease in all the Bradford constituencies, with Bradford West losing eight members at a decrease of 38 per cent, Shipley losing eight members at a reduction of 25 per cent and Bradford South losing four members at an overall reduction of 10 per cent. Bradford North has increased by one member.

BNP leader Nick Griffin claimed that the leaked list was a forgery.