Q. I have a 1yr old border collie who gets loads exercise but barks constantly through the night.she stops if u get up and sleep downstairs with her
A. Sounds like a little bit of separation anxiety. Going to her in the night is sort of a reward: she barks, you come. She is training you. You'll need to change your tactic to win this one. Sounds like waiting her out is not an option, she will just keep on barking.
I would still increase her exercise as that will help get more of the edge off.
Exercise is great, and you'll need it a great deal of it to play out a BC, but also remember that to truly a tire a dog out, they need mental stimulation. A Mentally and physically satisfied dog is a tried dog, and tired dog is a good dog. BC are extremely intelligent so you'll need some good games to play: try food dispensing toys, hiding food/treats in the house, adding some jumps (over benches, onto a wall or rock) while on walks, practice some commands etc. Maybe enroll in an agility or fly ball class with her. They are great fun and gives her a healthy outlet for some of that pent up energy.
You may also consider letting her sleep in your room. If you don't want her on your bed, maybe provide a crate so you each have your own space. It's a quick and easy fix if you are desperate for a solution.