As for the above statement that the royal mint asked for the undated coins back , I consider this a load of rubbish the mistake was first noted in numismatic circles about eight months before all hell broke loose with the london mint office announcment to the public .
It is thefore likely that the royal mint knew about the mistake and accepted the idea the coins were in circulation and worth face value
There is not a cat in hells chance that any undated 20p coins would have sat in a bank vault for that length of time - they all ended up in circulation - I myself found four or five before the london mint office announcment , i only ever found one more in circulation afterwards.
I would be interested in a copy of this bank letter but I strongly believe it does not exist as, the cat was allready out of the bag , horse had already bolted, a good eight months beforehand