Before the days when foxes started being everywhere in suburbia, there was a family of them at Twickenham in the grassy wasteland between the up line and the line coming over on the bridge from Teddington. They would often sit by the track in the sunshine, and, if the pups were there, attract attention from the passengers passing by. These days, foxes are so common that nobody takes any notice of them.
Years back, birds would nest in considerable numbers up in the roof at Waterloo. In quiet periods, their tweeting could easily be heard. The relevant authorities must have dealt with this, as I've not heard any birds tweet there for a long time. I've often noticed wagtails hopping around at Clapham Junction, mostly on the Brighton line and South-Western main line platforms
Going back some years, I saw a big rat running along the platform in the evening at East Croydon and at Vauxhall. I also saw one during the day at Earls Court (District Line); it ran along the side of the track then nipped up an empty cable duct under the up platform. I've not seen for several years the little dark grey mice on the track at tube stations; do they still scamper about or have they been removed?