Here is a nice male adder, which has recently sloughed (shed his skin). He was in a gorse bush and it was quite tough to get close, but I managed it without disturbing him. This is where a long lens comes in handy, even if it is very hard hand holding with gorse spines sticking in every part of your body!
The trick is to creep up on them, very slowly and very quietly! Ignore the spiders running over your face, don't jump if you are bitten by something, or spiked by a spine or bramble and don't make eye contact as they will always win!
Piece of cake - Not!