Just a thought about the 80s and the Yugoslav charter airlines practically having the market to themselves. For a spell in 1983, Britannia Airways operated a series of flights to Pula from Leeds Bradford (before the runway extension was completed). On every flight they used the same aircraft, a 737-200 dry-leased from Transavia, reg PH-TVP, painted in an all-white scheme. I don't know which tour operator was behind these flights but I would guess Thomson, probably testing the market or daring to queer Yugotours' pitch !
It was to be another two years before Yugoslavia was to be served from LBA again, but this time in the guise of JAT 707s and DC9s.