Thing is, and leaving aside the outside chance of some item of wildlife eating your face at 3am, you're pretty safe almost anywhere once it gets dark.
The countryside is very big, and one's capacity to be seen/found is very small after dark, so you're probably safe on the field-side of any hedge. After June, you often have straw stacks in fields that are comfy, and although exposed, are actually warmer on a still night than nearer the ground.
Any small copse of trees is also ideal. I sheltered from a heavy snow shower a couple of weekends ago, in a close planted copse of pines. The cover was brilliant; I could have hunkered down there in a bivvy for a few hours, no problem - and there's no chance I'd be found.