Welcome to Flyertalk cambridge.joe, welcome in particular to the BA Board.
Originally Posted by
cambridge.joe
1) So I'm on BA441 from AMS, am I correct on thinking if I were to take BA440 from LHR it would be fine to reboard the plane regardless of delay?
BA440 turns into BA441. You can check that via Flightradar24, here's an example (this link won't work after a few weeks):
http://www.flightradar24.com/reg/g-euuh
You find it by searching for a recent BA441 then clicking on the aircraft registration.
So if BA440 is late, then BA441 will also be late. AMS decants arriving passengers directly into the departing passenger area, no security, no passports, so reboarding will be straightforward. This is 99% plus position. There is a very small risk that BA441 will go technical on the return and therefore you get shifted to another service, but your booking is still protected in that unlikely scenario.
Originally Posted by
cambridge.joe
2). If BA440 is delayed/cancelled then presumably BA441 will be delayed/cancelled would I be able to board my HKG flight from LHR or would I have to still run the LHR-AMS-LHR part?
In theory they could ask you to go to AMS and back, and then get rebooked, but in reality several FTers have been able to drop the AMS sectors in that situation. You can argue it on the basis of forgetting your first booking, and for the second booking you made alternative arrangements to get around the cancelled BA441 AMS-LHR. You need to check that the rest of the trip is not auto-cancelled, including a few days before your return services.
Originally Posted by
cambridge.joe
3) If I were to choose an earlier, cheaper BA flight to AMS would my next part of my trip be safe?
No. You can of course book the AMS turnaround for the previous day just to give yourself more margin, that's a really safe way of doing it, you just need to ensure AMS-LHR gets you to London under 24 hours before the HKG departure, which due the late departure time of HKG will be tricky but works for other destinations. If you do this in the morning you should be fine.