After taking a picture rail down its left the walls a little uneven would a thick lining paper disguise this or would it be best to rub it all down first? tia
I think you'd be very lucky not to see the creases through the paper. Simple polyfilla and a good going over with an electric sander would probably be best.
How well the rub down goes will depend on the material used to plaster with. It may be best to get a professional skim the walls.
Walls are a little uneven anyway. When I removed the thick painted paper from my last place there was a raised area where the old picture rail had once been. That paper had worked for years making it less obvious before I opted to strip everything down and found out what the multitude of sins were.