Thank you all very much for the amazing amount of answers in so short a time.
Anna: Thanks for the information about the Time Life book and the hint to the late Major General Riou Benson. If my memory doesn't play tricks on me it is through him that the manuscripts on Edward Riou have passed to the National Maritime Museum - perhaps they also have additional information on the picture. Another branch of research.
With regard to Bridgemanart and the Bourne Gallery, I already had contacted both of them. Bourne Gallery very quickly answered my inquiry, however they had to tell me that the picture has left their custody years ago and they do not know its actual whereabouts.
Tony: Thanks a lot for your biographical data, which are far more accurate and helpful than everything I have found on the net so far.
As to the scene depicted I am of similary opinion with devenish which is what roused my suspicion: Why would all the officers present have already raised their glasses, while Riou's own is still empty? Or put the other way around _ would the officer proposing the toast not wait until everybody present had his glas refilled before raising his own?
Another ploy would be the amount of empty platters etc. on the floor in the left foreground - not very navy-like in my opinion. What puzzles me also is the fact that most of the officers present are obviously just giving the toast (or might even be singing?) while Nelson, Riou, the Army/Marine officer and the midshipman on the left side remain mute. So the persons present seem to be in different states within the "toasting procedure". I have heard some artists have tried to put a whole sequence of events (like a short movie) into one picture. Might that be the case here? Refilling the glasses (Riou) - Proposing the toast (Nelson) while the audience is listening (Midshipman, Army Officer) - all the others cheering (rest of the assembly). Would such a style fit to the period in which Davidson was working?
The most detailed information I have found with regard to that dinner is the narrative attributed to Lt.Col. Stewart in "The dispatches and letters of Vice Admiral Lord Viscount Nelson with notes by Sir Nicholas Harris Nicolas".
Quote:
As soon as the Fleet was at anchor, the gallant Nelson sat down to table with a large party of his comrades in arms. he was in the highest spirits, and drank to a leading wind, and to the success of the ensuing day. Captains Foley, Hardy, Fremantle, Riou, Inman, his Lordship's second in Command, Admiral Graves and a few other to whom he was particular attached, were of this interesting party...
In Stewarts "Journal of the Baltic Expedition..." the event is not mentioned. Might M'Clarke/Arthur, for whose work above quoted narrative was written, might have lend a hand again?