Can't speak to tbe laws in the UK, but there are places on the USA where the double-line "NO PASSING" zone has an exception, when drivers can CAREFULLY pass a cyclist despite the no-passing. If that's not the case in the UK, then the cyclist was right. Passing while staying in tbe SAME LANE is DANGEROUS. Unless the land is extra-wide (rare over there), a driver CANNOT pass and maintain proper legal separation.

Safe-passing laws for cyclists do not reduce their rights when circumstances work against drivrs.