Invicta did a lot of ad-hoc work, picking up flights on behalf of others rather like Titan today. A I have mentioned before quite a bit passed to them after Court Lline went bust- Court Line flew for Jetway, Pontins, Warners etc. as well as in house Horizon and Clarksons at the end.
Passengers who had booked expecting a nice new One Eleven thus ended up with the dulcet tones of four Rolls Royce Tynes for three hours down to Alicante on a Vanguard in September '74.