I don't think you really needed me at all! I can add little to what's been submitted so far. There really was an action between Nottingham and Mars as Teribus says. The Saumarez family (variously de Sausmarez, Sausmarez, Saumarez) were a quite famous Royal Navy family originating from Guernsey. Eventually there would be two destroyer flotilla leaders named HMS Saumarez (one in each World War) when it was the fashion although I assume that the vessels were in fact name for the later Admiral James Saumarez. Captain Phil would probably be called Sausmarez.

Ships sailing under false colours or unidentified: This was pretty normal - there was no need to identify your ship and it was a valid 'ruse de guerre' to hoist someone else's if there would be some advantage. A 60gun ship like Nottingham could perhaps be taken for a large merchant ship, although it would be an umusually large merchantman or privateer. The HMS London of the period would be unmistakable as she was a three-decked line of battle ship. Of course the version mentioning the ship 'London' could have be a privateer - Liverpool sent out many privateers.