Definition of "swifty"

I have just enough time for a "swifty" in the reopened (but on this day just about to close) '301' bar on Platform 4 before boarding a two-car Northern Class 158 working the 1824 to Leeds. [In this case, meaning a quick beer.]

2022 November 2, Paul Bigland, “New trains, old trains, and splendid scenery”, in RAIL, number 969, page 57