A current chart is a legal requirement, it can be CAA, Jeppessen, or some other publisher if it's current and complete.
There is no requirement about scale and indeed, many pilots of slower flying machines (gliders, microlights, helicopters) much prefer the CAA 1:250,000 which is absolutely fine.
I have seen some pilots fly with 1:50,000 Ordnance Survey maps, suitably marked up, and that's perfectly legal also. In fact, I think that the RAF and Army supply them like that to helicopter pilots.
G