So, returning to the original question: The point has been made several times in this thread that drink and song have always been close partners, so the question is incapable of producing a simple answer. I find a more interesting question to be: 'For how long have pub singers required electronic amplification in any room larger than a broom cupboard?' - but no, I'm just coat-trailing.
If what we are searching for is the origin of more or less organised song sessions, we still have to go back a very long way. The tradition of private dining and singing clubs meeting in taverns was solidly established by the seventeenth century and must have had a long back history.
It should be a bit easier to trace the emergence of more formal chairman-led pub concerts in which the majority of the people present were members of an audience enjoying performances by professional and semi-pro vocalists, rather than being themselves participants (other than by providing additional volume for choruses).
Pub concerts of this kind were numerous by the 1830s and their history as forerunners of the music halls of the 1850s has been told many times, but they already existed, fully formed, in the mid-eighteenth century. The 'Comus Court' of the Choice Spirits Assembly flourished in the 1760s at Jack Speed's tavern in Fetter Lane, off Holborn, and it seems to have been active for several years before and after that time. The Spirits, who occupied the top table, was a group of entertainers, who included two of the most distinguished legit theatre vocalists. Many pocket songsters of the period contained songs (some of them very near the knuckle) attributed to members of the group.
This pub concert was certainly not the first of its kind.There are discoveries still to be made in this area.