Is it against the law in the UK to park on the public highway?

Answer 1

Parking in highways is usually prohibited except for emergency cases only.

Answer 2

If, by highway, you mean motorway (equivelant to freeway), then yes, it is illegal to park here (unless in emergency), because of safety reasons. There have been many instances of cars parked on the "hard shoulder" being struck by fast moving vehicles.

On other roads, such a A roads, parking is permitted, but restrictions may apply, for example double yellow lines by the side of the road mean no parking, and zig-zag lines approaching a pedestrian crossing also indicate this.

For a more comprehensive explanation, I recommend you buy a copy of "The Highway Code", a government produced booklet, available from most bookshops in the U.K. (and possibly online, try Amazon).