I have begun looking at the London based festival Japan Matsuri. I have started with their website, which at present has limited information on it, and their Facebook page.
The word Matsuri means festival or holiday, and the Matsuri was historically sponsored by a shrine or temple as part of the practice of "Honouring your Ancestors". Matsuri 2012, which is to be held in October is only the fourth festival running, so it is quite new.
Considering that this festival has been running since 2009 I have not heard of it. According to the website, they do have a good turn out each year, however as a Londoner I feel that it's bad that it didn't reach as far as me. This is be something I would be greatly interested in going to if only I had heard of it without going into great research.