Airtours charters were always announced as Tango, for a reason I never understood, there used to be cards up at their desks at Gatwick advising that PA's for departures (remember those ?) would call the flights using "Tango". I used to think it must be their callsign but this was apparently "Beatours", which must have sometimesgot mangled a bit by overseas ATC !
Airtours seem to have been just about the only UK charter operator to do holiday runs to Eastern Europe in socialist days, which were otherwise invariably done by charters from the relevant national airlines, Balkan for Bulgaria and several locals for Yugoslavia. I presume the tie with British Airways, who those airlines would be in pool with for schedules to London, helped this.