Need Help!

[FWK]

Were it not for your location having been set to the UK I'd be very confident that this is a Brown Snake (Storeria dekayi), but if this animal was indeed found in the UK then it must be a Grass Snake (Natrix natrix) as Rubbertoes suggests. If you would confirm you location we can be more sure of what you little visitor really is. I'm still thinking it is a Brown, in spite of what you have your location set to. Either way it is absolutely harmless and very cute, thanks for sharing.