A good site for identifying dragonflies in the UK is Dragonfly Identification UK
I took some photos of a Common Darter Sympetrum striolatum, I saw a number these dragonflies around the ponds and marsh area at Barnes Meadow, Northampton: Wildlife Trust Barnes Meadow
You should be able to see these dragonflies from May into November. A good place to look is around ponds & still waters, if you have a pond in your back garden then you have a good chance to see one visit.