This poor thing was picked up outside work today by one of the staff, as you can see it has had some form of an accident, it was quite large and as you can see it has the most vibrant markings.
I looked it up on internet searching for UK Dragonflies and this is the information.
"have long thin bodies, four large wings that are held out to the sides and two large compound eyes. Antennae are very short. Southern hawkers have black bodies spotted with green, males also have some blue spots near end of their abdomen.