Basil,
You may be right, but I was wrong. The Bloomberg article, linked above, shows that STN contributed £31.5m operating profit out of £108.2m group operating profitin the 6 months. (not revenue, as I stated).
This means that op.profit of STN was 29% of the total, for 40% of the pax. Even worse for MAG, as they have to service their debts from the op. profit.