There is no British netroots, and God forbid there ever will be.
Why? Well, the original thing is/was an effort to mobilise the grassroots support of the US Democratic Party, to shove in the underpinning of a mass party that it doesn't really have. This was intended to a) supply activists and donations, and b) exert a leftward pressure on the party leadership. This doesn't really translate in British terms, because British political parties are much more substantial organisations than the US ones.
Not only do they have long-term mass memberships, they have a professional organiser caste and an ideological history. They also enjoy much more tribal loyalty. What worries me about any attempt, as Sunny "Pickled Politics" Hundal seems to want, to lash the Internet community in the UK to any one political party. In the US, the problem is that one party has gone berserk and dragged the Overton window off across the countryside with it. The corrective is to whack it in the teeth.
In the UK, the problem isn't one of Westminster democracy but Whitehall and off-Whitehall democracy, something we've arguably never had. (Pickled, by the way, is doing something useful in being a much less London-focused blog, but that's for another time.) I would far prefer that blogs stayed like Lawrence's army - "a thing without front or back, drifting about like a gas", agreeing on a few but powerful rules, trying to enlarge the zone of sanity.
(PS, the other night I met Daniel Davies, Tess, and Sunny. That would be Dsquared, Shesquared, and Psquared, right?)