I do not think the Harry's Place bog has any impact on world politics. If it did, more people would be aware of it. I have never even heard of the blog until I just read this question and did a google search. It would have to gain a lot more popularity.
Social media such as reddit, twitter, and facebook, as well as major news websites have left very little room left for blogs such as Harry's Place to make a big splash in the world politics. The Internet has grown and with it has grown vast number of websites that cater to a more massive crowd and massive voice to which popular media and, subsequently, world politics keep a sharper eye on. Discourse done at this blog is also done by social media, with the backing of many people from all walks of life and perspective at various social media sites such as Farheed Zakaria on facebook and even prominent political figures themselves on reddit, as an example.
Harry's Place is only known to those in the UK. Since it is extremely critical of the UK government, it often is overlooked by the international community, much like the Westboro Baptist Church in the US. He may make headlines in the UK, and influence some foreign policy through the UK, but Harry's Place will rarely make headlines on its own without the UK.
I do not think that Harry's Place blog has any impact on world politics. While it is a blog that is famous and popular with a lot of people. I do not think that is has any significant impact on the politics on the world stage. I personally don't really read the blog because it doesn't interest me.
Harry's Place blog is virtually unknown to the people of the world. The blog is run out of the UK and usually covers politics there. Most people of the world are not concerned with the fine tunings of the UK government, so Harry's place blog doesn't have any real prominence.