If I see one more post about cheese and holes I'm going to vomit. What a worn out cliche.
The flying over London argument is irrelevant in my book.
With your logic the Captain would have to get out of the aircraft after the baggage doors were closed and the refuelling finished and do a walk around to check up on everyone just before departure on every single flight. If another department is working on the aircraft just prior to pushback the flight crew have to trust them to do their jobs to a degree. That's just modern aviation. You can't know for sure that they have " done their own diligent external check", you have to trust that as professionals, they have done their job. You're living in a fantasy land.
Now that's an appalling indictment of modern aviation. That's just the way it is so you just have to put up with it? If that's the way the guys at the front think these days then I grieve for the industry.
And as for "you have to trust that as professionals, they have done their job", could you please explain the pre-flight walkround check as printed in the FCOM and the crew responsibility for actioning said check? In particular, the item that the Fan Cowl Doors are closed and latched.
I agree the crew did a good job in bringing the aircraft back to LHR but rather too much of the arsonist joining the fire brigade for my liking?