Orion UK (KG) was formed by Horizon Midlands Holidays who had survived the Court Line crash in 1974 and went it alone, whereas Horizon Holidays and 4S Travel did not.
In 1989 Horizon Hols (they had dropped the Midlands by now) was bought by Thomson Hols and the KG fleet was merged into Britannia/BY who did not want the A300's and
AFAIK did not operate them as BY flights.
The 737-300's were painted in BY livery but were not kept for that long.
There was a USA outfit also called Orion who leased some dodgy old 747-100 crates from Cargolux op'g for Airtours International and ICA (Barbados)
(Cargolux also leased 747-100 to Lion Air also op for Airtours)
Re QTV - Ah yes I should have got the ''TV'' as Treviso, I did wonder that ~~ Also back in the early 70's Reus was known as QGN (Tarragona)