That was the successful bid at auction yesterday for the letter written by a former ally of the rebel leader who decided to inform on the Big Fella in 1919 shortly after the British declared the first Dáil illegal.

Adams auctioneers had put a value of between €2,000 and €3,000 on the one-page letter dated Nov 11, 1919 and sent from 21 Gardiner Place, Dublin.

Signed by a H Quinlisk, who had a personal gripe against Collins for refusing him further handouts after he squandered cash at the racetrack, it was addressed to The Under Sec, Dublin Castle and marked “secret” and “very urgent”.

Quinlisk wrote: “Sir, I have been forced by circumstances to write to you. I would have come personally but if I were seen entering the castle my life would perhaps afterwards be in danger. I was the man who assisted Casement in Germany, and in coming home I have been connected with Sinn Féin. I have decided to tell all I know of that organisation and my information would be of use to the authorities. The scoundrel Michael Collins has treated me scurvily and I now am going to wash my hands of the whole business. If you accept my offer, please send a man, one who can be trusted, to the above address on tomorrow evening at four o’clock. I am living there under the name of Quinn. I am yours faithfully. H Quinlisk, late Cpl Royal Irish Regiment.”

One of Collins’ spies in Dublin Castle intercepted the letter and a trap was set for Quinlisk, who was taken away and shot when he turned up to watch what he thought would be Collins’ arrest.

The letter was only briefly referred to in two historical accounts since and its full contents were not known until it turned up in the private papers of a woman who had connections to Cumann na mBan.

Quinlisk’s death warrant, as his letter turned out to be, was just one of several hundred items of political and military history put under the hammer.

The top lot was an original copy of the 1916 Proclamation which sold for €96,000.