In another sign of its remarkable growth, UKIP has just announced that it now has 30,000 members, an increase of 8,500 since March.

The party's next aim is to overtake the Lib Dems, who were reported to have just 42,501 members at the end of 2012, a fall of 35 per cent since 2010 since 2010 and the lowest annual figure in the party's 23-year history.

Conservative membership figures are notoriously hard to access (the party doesn't hold a figure centrally) but recent estimates suggest that membership has fallen to a record low of 130,000-150,000 (down from a peak of 2.8 million in 1953). Membership briefly rose after Cameron became leader in 2005 (from 258,000 to 290,000) but has fallen ever since.

Labour has now supplanted the Tories as the largest party by membership, with 193,000 confirmed members at the end of 2011, up from a record low of 156,000 in 2009. But that is still down from 405,000 in 1997 and from an all-time peak of 1.015m in 1952.