I remember as a boy (16yo), in 1966 working for an ad agency and delivering some artwork to a location just to the extreme left of St Enoch's, within the arches, many of which were shops etc.
These units however were limited height access and opened into vast, and I do mean VAST caverns full of Really Big wooden barrels.
So, I assume there was either a whisky warehouse, or a sherry warehouse there which went back the entire length of St Enoch's, towards Stockwell Street, and beyond.
Wouldn't surprise me if still there................?