We did have to check this was not an Adder (they're the one venomous native snake in the UK but rarely seen (very shy) and even more rarely in gardens. In all my life I have only glimpsed three Adders and then briefly as they quickly slide off. But no, this was definitely a Grass Snake, which is non-venomous. Apparently they can grow to two meters long. We reckon this one was about 2-3 feet in length, so maybe still youngish. Their one defence, a last resort as they prefer to keep away, is to excrete a smelly garlic-like fluid from their bottoms. Hmmm, something to avoid!
So - happy as we are to have this newcomer, we are also a bit concerned because the main thing Grass Snakes like to dine out on is frogs and toads. We have a very healthy population in our big pond, small pond and polytunnel pond, all helping to keep the slugs at bay. We'd be pretty unhappy if they all got gobbled up but hopefully the whole food chain should keep in some form of balance.