No, not joking. As I said, thought it was a body at first - as the person was curled up on the back seat with my yoga mat on top of them.
Re-locked the car, yelled my husband to call the police. He said "I dont know their number" (I promise you.....
).
He pottered down the garden to my car and peered in with me, by this stage the 'body' was beginning to sit up. I asked her WTF she was doing in my car, she said 'well it was unlocked'. Told her to get out, so she staggered out, then tried to stroke my dog (I kid you not), at which point she was told to start walking. Fast.
Very strange as we live in the middle of nowhere, in woodland, up a track off a tiny lane.
Looking back, am starting to see the funny side 
Oh and no, DH, I wont leave my car accidentally unlocked again, as he so helpfully suggested.