Do I have to go through customs in London if I fly from Edinburgh to Paris?
 

Traveling with my family of 4 in March of next year, and trying to decide if on our Edinburgh/London/Paris trip we should fly from Edinburgh to Paris, then hit London on the last part of our stay. I can get a really cheap one way flight on British Airways, with a stop in London... but it has only a one hour layover. Will we have to go through customs in that hour?

The best thing to do is contact the airline. I *think* Edinburgh to Paris is a domestic flight, but I'm not certain enough that I would count on that!!

EDI to LHR will be a domestic flight so you'll arrive at the domestic part of Terminal 5. There is no passport check when leaving UK and no customs but you will have to go through security to get to the international departure lounge, where you catch your flight to Paris. 1 hour should be sufficient at LHR. If by any chance your incoming flight is delayed, you will be transferred to next available flight free of charge.

Is it cheaper than flying direct from Edinburgh to Paris with Easyjet or Air France or FlyBE?

As for OP - Edinburgh & Heathrow are in the same country, so there's no "customs" (sic) check any more than there would be flying between Chicago and New York.

Even if Edinburgh & Heathrow were in different countries there would be no "customs" check as civilised countries allow airside transfers eliminating the need to pass through "customs".

Americans typically call what we would call passport checks as 'customs'.

You shouldn't have to but... every time I've flown from Edinburgh to anywhere abroad, via Heathrow or Gatwick, in the last few years, we've had to go out through security & back in again. And coming back in, we are mixed in with international transit passengers so there can be long queues. I think the officially recommended minimum time is either an hour and a quarter or an hour and a half - I wouldn't attempt it with less than an hour and a haf or preferably 2 hours.

Agree with the suggestion to look at Easyjet direct flights.

If you do do travel via London, bear in mind you won't be able to take any liquids bought after security in Edinburgh through security in London, unless they are in sealed 'duty free' shop bags.