The problem found in the mid-70s was that whilst TB control measures were working across most of the country in these small pockets there remained to be high incidents. Higher levels of disease in cattle mean that cattle to cattle infection will have had some influence upon this, but it is thought that there must also have been additional transmission.
As found today these pockets of land are ideal environments for badger habitat and these areas still had higher badger populations than other areas which were much lower than are seen today as populations were controlled, and also the rise in popularity of the car had a very large impact on their numbers.
It therefore appears that whilst the cattle controls worked well in areas where the badger population was lower it appears that they did not work in areas where the badger population was higher. This period coincided with a couple of major influences upon TB control in that it was also the time that badgers were first implicated in disease transmission and also the introduction of the first badger protection legislation. We cannot say definitively for how long before this badgers played a role in TB transmission but one would suspect that they have always done so and that it is the higher numbers we see now that have contributed the greatest. Whether in these pockets it was due to cattle to badger reinfection or badger to cattle infection we are unable to say but only draw some conclusions that in these areas where badgers were reasonably plentiful the infection in cattle remains. Gloucestershire is still today the county with the highest number of Confirmed Herd Breakdowns.
The original legislation to protect badgers introduced in 1973 can go some way in explaining as to why disease incidence was not further reduced as populations were allowed to grow in these hotspot areas which continue to be ideal areas with plenty of pasture land and plenty of hedgerows to support large social groups of badgers. The increase in badgers populations was noted in the last major survey which can be found here - http://jncc.defra.gov.uk/page-2797.
The following link is to a paper upon the contribution of cattle to cattle transmission which you may find of interest, whilst we do not suggest that this route of infection has no part to play it is clear that there are other influences upon disease levels. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2366193/ .
I hope that this helps to answer your question slightly, and I apologise if it does not. There are no definitive answers to your questions I am afraid but experts agree that badgers played a role in these areas, their protection prevented their control and therefore the control of disease in their populations, and cattle controls alone were not enough to deal with reinfection from this external source.
There are so many different facets to the current bTB crisis that making any sort of informed opinion is at best difficult and at worst so confusing as to be fatuous.
My personal opinion is that ultimately, a vaccination programme for livestock (and maybe for badgers) is the only sensible solution; which means, of course, that politicians in this country and the rest of Europe need to stop running about like chickens with their heads removed, and produce a sensible long term, science based policy, rather than short term politically based solutions.
It is possible that, because of the current situation, some limited badger culling may be deemed necessary, but it's only ever going to dull the edge of the epidemic. I would recommend that in order to form your own opinion you digest as much available information as possible and a good place to start would be at www.warmwell.com and in particular this government report
I also believe that the issue of trace element deficiencies may well prove to be a key factor in a long term solution.