For 742 crews in UK - There is always the possibility that it is Air Atlanta Iceland.
After all, they operate from Gatwick and Manchester for their pax charters.
Further, majority of their pilots are from UK, their Flight Ops Management as well.
So, they tend to favorise the UK guys.
Besides that, they operate freighters in the Middle East and South Asia.
Then... could be Air Atlanta...?
xxx
Happy contrails