Shocked to discover the record shot I took of a dragonfly at Burnham Overy Dunes was a female Vagrant Emperor (Anax ephippiger) on 25th October 2016.
Just in case it may be still there and someone wants to have a look for it on the next warm day, here is some further info
I think I saw the Vagrant Emperor intially immediately NE of Gun Hill favouring an open area with a scattering of privet. I put it down as a Migrant Hawker, as I never saw it perched, but did mention to two other birdwatchers there, to keep an eye open just to make sure. I couldn't get a photo as it was extremely flightly (rather like the Isabelline Wheatear there at the same time)
A couple of hours later I bumped into a dragonfly that I did manage to get a poor photograph of and which I presume was the same dragonfly (it was equally flighty and looked similar in flight). It was favouring the marram to NW of Gun Hill but keeping to the lower 'shelf' area between beach and first dune ridge. So 2-300 hundred meters from the potential initial sighting.
It always perched fairly low in the marram and was easily spooked.