I think it's a little harsh to judge what was done more than 40 years ago by today's standards. Miss Badham and Miss Evans were petshop keepers whose hobby expanded into a zoo. It couldn't happen today and it should never happen again.
They treated their animals in the way that seemed right to them, as did John Aspinall, Leonard Williams, Len Hill and many other 'eccentric' animal keepers. And like those other aspiring zookeepers, we can now see (with hindsight) that they each got some things right and some things wrong. Those Brooke Bond adverts paid for their zoo (and I suspect that many of the other zoos in the country would have done the same for the money).
We can't change the past. Twycross Zoo must be judged now on what it is today and how the management and staff are working for its future. It aspires to become the World Primate Centre - but there is a lot to do before that title holds true (in my opinion).
Alan