OzzyHugh:
Following on from above post - I tracked the original photo and, believe it or not it was from 1970 at Royal Lancashire Show - so maybe it was 1971 that reflective marker boards appeared .Hugh
I remember that they were beginning to be fitted to existing trailers in 68 69 and new ones had them in 70 so maybe it was the 68 transport act that brought in speed limits and licencing etc , that changed the law