I had one on the front of my garage last summer. It flew off before I could get a picture, but it was a good 3" long.
Googled it later and it was likely an Asian hornet. If I'd have got the picture, I could have reported it to someone, as I believe they are trying to nap the hornet's progress across Blighty.
Also, heard on r5L the other day, about seeing wasp traps in your garden, to discover which species are where.