I believe buses have been banned for a long time, however, I don't think it would typically be enforced, nobody walking up and down the buses checking this on the likes of Victoria to Glasgow... Even back when I travelled that route regularly in 1987. Think it was illegal then.
It isn't banned on the train, though local bylaws can change this due to football crowds, and they've got a late night ban on scottish trains now (all across scotland or just some area, not sure). They serve you it in first class rest of the country, and indeed, the late 11:23pm Euston to Wolverhampton is train still serving drinks past midnight...
I've not done overnight trains since the 90's and breakup of the joined up sleeper trains not going via London. Back when I did I think it was mandatory that there was a blottoed scottish bloke on there, ranting and raving. Except that one time, except in retrospect, I suspect it was me...