We're told the ultimate cause of the McBride fiasco was that the Labour party feels threatened by the existence of "right-wing" blogs, and is trying to redress the balance.
I don't really think there is much of an imbalance to correct. The Conservative party has Iain Dale and Tim Montgomerie, but that's about it. The important blogs are the ones that fill gaps left by more prominent outlets. Guido is right-wing, but he isn't Tory. The effect of a Labour party blog would be negligible compared to, say, www.guardian.co.uk , and the Tory blogs are insignficant compared to www.telegraph.co.uk .
Now it's true that among political groups unrepresented by the mainstream, Libertarians are much better represented than, say, Marxists or nationalists. Given the tendency of the centre-left to label even Devil's Kitchen as "Tory", what looks like a Tory bias is mostly a Libertarian bias.
Why are Libertarians better represented than other non-mainstream groups? One answer is that technologists are disproportionately libertarian, and libertarians are very disproportionately technologists. That has always been true - I came to libertarianism via Usenet, and those people now all have blogs. That is less convincing as a reason than it used to be, as the technological bar to clear to get a blog presence is now negligible, compared to when Samizdata and Instapundit started up. There could still be momentum from that early lead, but I think it's small.
I think it's more that they are just closer to the mainstream. Also they have fewer existing organisations - Marxists and nationalists have the SWP and the BNP as long-standing centres to organise around.
Consistent with this, the Liberal Democrats seem to me to be strongly represented in blogs. That is to be expected, as they are mainstream but do not have the resources of the two main parties, particularly in terms of friendly press outlets.
Parallels with the US are confusing. The big difference there is that they do not have nearly as strong a right-wing sector of the mainstream media as Britain has with the Telegraph, Mail, Sun etc. You also don't see monolithic party machines as we have here - their parties are fragmented geographically, and at the end of the day answerable to Primary elections). So when you look at the US, you see a strong right-wing presence which is very much mainstream Republican. Here we see a strong sort-of-right-wing blogosphere, which consists in fact of dissidents from the Conservative party. At a glance, there seems to be an equivalence.
At the end of the day, the Labour party doesn't need Labour List, Red Rag or anything like them. Their blog presence will flop not because they're doing it badly, but because it's redundant. They have the Guardian and the BBC.