I think that there are two issues being confused here - (a) the elimination of brake vans on goods trains and (b) the doing away with guards on trains. The first, elimination of brake vans on goods trains, was, as has already been said, brought about by the introduction of fitted wagons on goods trains. When this happened the guard rode in the locomotive in, I think, the leading cab. The use of a brake van on a nominally fully fitted train would, I think, have indicated a problem with the brake system. The second question - doing away with guards on trains - depended on the availability of train radio on various lines. In the event of a train failure one of the guard's duties was to assist the driver in protecting the train and until there was a reliable method of doing this without the need for a second man the guard remained. Of course there were union issues in both cases but mainly in the second case where there was a reduction in jobs.