Don’t know, but they had the brilliantly named “Operation Hope Not”, preparations for the funeral of Winston Churchill. It started in 1953; he died in 1965 (https://en.wikipedia.org/wiki/Operation_Hope_Not)

There also is “Operation London Bridge”, a plan that has been updated for over half a century, for when queen Elizabeth II dies (https://www.theguardian.com/uk-news/2017/mar/16/what-happens...). That will be a momentous event because because she’s the queen of a very large part of the world (Australia, Canada, New Zealand, Papua New Guinea, the United Kingdom and various smaller islands), and because most of the population of Britain wasn’t born when her predecessor died (making it a rare event)