Well I never ...
Interesting Wikipedia Article on RN "Fleet Tenders" which in fact were three dummy battleships (HMS Resolution, HMS Revenge and HMS Anson) and an aircraft carriers (HMS Hermes):
https://en.wikipedia.org/wiki/Fleet_tender
I had heard about HMS Centurion pretending to be HMS Anson in the Mediterranean however teh others I knew nothing about! The only other "dummy" battleship was the WWI fake HMS Audacious which was faked after the real battleship foundered on a mine in the early days of the war.
I followed this thought up to the following link (apparently there were 14 mock WWI RN Battleships:
http://www.gwpda.org/naval/dummybbs.htm
https://www.amazon.com/Liners-Battledress-Wartime-Camouflage-Passenger/dp/0920277500