The 25th Anniversary story "Silver Nemesis" featured considerable location filming at an disused gas works. In the 1990s the gas works site was destroyed and the Millennium Dome was built on the site.
German actor Anton Diffring admitted in an interview during production that he had never seen Doctor Who, and was completely baffled by the whole project. He accepted this role so that he could be in London to watch the Wimbledon tennis tournament.
Although Anton Diffring played Nazis in many film and TV productions, according to Chris Clough on the DVD commentary he fled Nazi Germany because he was liberal and gay.
This is currently the only anniversary special in the series proper that is isn't a multi-doctor special.
Producer John Nathan-Turner wanted a bigger budget for this story because it was the 25th anniversary special, but this was rejected by the Controller of BBC One, Jonathan Powell, who was well-known for his dislike of the series.