It's all about Risk Management
The BA777 is designed, maintained and operated such that the loss of one critical power unit does not result in the loss of the aircraft (and the subsequent collateral damage on the ground). The Hawk, however is designed, maintained and operated such that the loss of the critical power unit will result in aircraft being lost (with the subsequent collateral damage on the ground). Such is the way for both aircraft for good reason and I do not challenge that.
Indeed, the BA777 can suffer a multiple system failure and fall upon us; we as society choose to wear that risk in return for joy of air travel. Equally, we as a society choose to wear the risk of a military jet falling upon in the interest on National Security.
Rightly or wrongly, London has special rules regarding Single Engined Aircraft and OC Ops has some discretion on that. It's not for him, you or me to challenge those rules; but two questions for you;
1. Does a Hawk coming into Northolt enhance National Security?
2. OC Ops has to weigh up his career/ possibly his personal liberty against the strength of an Adour fan blade.... how strong is that blade?
So "old chap" it comes down to risk and return.... OC Ops seems to be wearing a lot of risk for not a lot of return...