It's in Danbury in Essex, National Trust reserve, a place quite highly populated with Adders. Last year I shot these with my SLR
I prefer to shoot from a distance to avoid disturbing them too much but they soon let you know when you're not wanted!
p.s males are darker than females. Their Bite can be quite nasty but only deadly if you've a particular allergic reaction to them. You'd have to be pretty stupid to get bitten by one though, they deserve respect and protection.