I don't think that Harry's Place is particularly that controversial of a blog. Obviously there are people who are not going to agree with his political ideologies, but overall I think that it has at least a neutral if not a positive impact on British politics. It helps people hash out ideas.
I do not believe the Harry's Place political blog makes a positive impact on British politics. I believe the blog discourages compromise and makes it more difficult for the political system to work. It makes a point to be biased, which I think is a problem since people don't all seek out the truth.
Though popular websites can have an effect on politics, government and politicians, I think the effects are greatly exaggerated. Politicians use it as another tool to judge how people feel, but I don't think it really affects anything in a big way. I think that kind of change takes real action.
Having read just a bit of the Harry's Place political blog, I have to say that I don't think it has any meaningful impact on British politics. Most of what I've seen discussed there is just a reflection of current sentiment. It's more of a reflecting pond than an influencer.
Harry's Place blogs are much like Rush Limbaugh radio broadcasts in the US.Those people that already share that view are further exposed to propaganda and misinformation to reinforce their already skewed version of the truth. There is some impact, but not significant enough to change a swing vote. It just reduces the number of swing votes back to their party of origination