I saw this in my garden in South London from about 20 feet away, which says more about its size than my vision! It was around 6 inches long and I have NEVER seen a bug so big in the UK!! Sorry for the poor iPhone image but I had to get back to work and didn't have time to grab a 'real' camera! Any ideas what it might be? The closest I have found online is a Blue-eyed Darner but that is native to the west coast of the USA! Maybe this jetstream pulled him here?! Whatever it is it was brilliant to see it up close!!