Goldryder
65min should be OK if you go straight throught the system without getting distracted. As BA have sold you this connection, then they have the responsibility to look after you should it not work.
The key to T5 is "compliance". Shortly before you go through security your boarding card is scanned by a security bod. This has to be done before Departure time -35min for you to be accepted on to the flight. Miss compliance and you will be bumped off.
On your journey from NCE you will most likely arrive at a jetty on the main T5 building. Follow purple signs for transfers. At the transfer area there is a seperate set of counters for those connecting to domestic flights. There is usually a much smaller queue here. They will take a photo of you as you a going to be a domestic pax in a mixed international / domestic departure lounge. The photo is re-checked at the gate. At this point your boarding card is scanned for compliance. Follow escalators upstairs and join the queue for security. Once through security off to the gate
BA / AA / IB have recently started a process to help those arriving on delayed flights to catch their onward connection. Usually a message will be sent to the arriving aircraft to indicate that some passengers will be met by staff. They are met at the top of the arrival jetty by a staff member who gives them a "Express Connection" card. This is bright orange for visibility to other staff and allows queue jumping. I believe it also tweaks the compliance timing to departure -30min.
Have a good trip
