As the Greens continue to press their case for inclusion in the TV debates (with the self-interested aid of David Cameron), it's worth noting a potential landmark for the party: their membership could soon exceed that of Ukip. The latest figures, compiled by Adam Ramsay of OurKingdom, put the Greens' total membership at 40,879, just 635 behind Ukip (whom the broadcasters have, of course, invited to the debates). He calculates that "at the current rate of growth, the Greens will overtake Ukip within a week, and be ahead of the Lib Dems before polling day ". The party's membership has more than doubled since September when it stood at 20,000.

By contrast, Ukip's growth rate has slowed, with the party gaining just 2,514 members since June. The most recent figure for the Lib Dems puts membership at 44,576, a year-on-year rise but still well down on its 2010 level of 65,038. The greatest success story is the SNP, which now boasts 92,000 members (making it the third-largest party), an increase of 66,358 since the independence referendum. The party will now likely pass the 100,000 mark before the general election. And while the SNP will likely be excluded from any debates on the grounds that it is not a UK-wide party, it's worth noting that it is likely to hold more seats than Ukip after the election (it currently has six and hopes to increase that to at least 20) and possibly even more than the Lib Dems. 

Here are the membership figures in full:

Labour: 190,000 

Conservatives: 149,800 (224,000 including wider party). 

SNP: 92,000

Lib Dems: 44,576

Ukip: 41,514

Greens: 40,879

Plaid Cymru: 8,000

National Health Action Party: 4,691

English Democrats: 2,500

Left Unity: 2,000

Britain First: 800

BNP: 500