Is anyone aware. Specifically, in hallways. Is there a set distance between emergency escape lights in hallways? What British Standards or DCLGs would they refer to? Many thanks.

No, because different types, makes & models of fitting have different light outputs and so usually come with spacing tables to allow you to work out far apart fittings need to be depending if it's a corridor or open areas, you need 1lux, 0.5lx or 15lux/10% of normal light and if you are wall or ceiling mounting (with different distances for different height ceilings)