Entering Scotland, and Customs

[cessna152towser]

I've flown to USA and Canada and back via London Heathrow on three occasions with British Airways (once each to Boston, Los Angeles and Vancouver).
Leaving Britain is the easiest, you go through security prior to the domestic flight. Flying with British Airways you arrive at their domestic section of terminal 5 and then take a short trip on an underground shuttle train to the international departure section of terminal 5 where you go through passport control where I have never had to queue and there has been no further security check. Although I had allowed for a two hour connection, half to three quarters of an hour proved sufficient. Baggage is checked through to final destination and does not need to be reclaimed at Heathrow.
Coming the other way is less easy as you firstly have to clear immigration and customs where there are often queues, then they make you go through a further security check before you can join your domestic flight and there are often long queues for this. Going this way, meeting a two hour connection can be a tight schedule.
I would envisage Heathrow would be a lot of hassle if you used different airlines. BA's domestic flights use terminal 5 as do their Transatlantic flights but other airlines use a variety of terminals. There are free trains which link the terminals but sometimes you can have a 15 or 20 minute wait for one of these, plus if you are changing airlines you would need to reclaim your luggage and then check it in again.
If you can get a direct flight between USA and Scotland so much the better. I like the direct flight from Glasgow to Vancouver but unfortunately it only goes once a week and only during the summer months. It could be worth your while checking this out though. As the Vancouver-Glasgow goes over the Arctic the flying time is only 8 to 9 hours, plus say a couple of hours flight time from LA to Vancouver and you might find the total flying time is shorter than going from LA to London and then Scotland. Edinburgh and Glasgow airports are more customer friendly and a lot less hassle. Arriving back in Scotland directly from overseas I generally get through passport control without queuing (though my partner and I both have European passports which they prioritise). Following passport/immigration checks I have always been able to walk straight through the green (Nothing to Declare) channel of customs unchallenged.