Hi everyone and thanks for all your replies!
There's no way he would go if I asked him not to and he wouldn't make me feel bad about it at all, so it would be as much down to me if he missed the birth as him and wouldn't be something I would ever blame him about.
I know the trip is important for him and his business and whilst someone could go in his place it would be preferable for him to go but he has said there would be no question of him not getting the first plane back if I went into labour - although I explained that I may not just be able to keep my legs crossed until he got back 
My three siblings all went over due date and I was born on my due date. My eldest sister went over with her only dc and my other sister was a week early with her first and late with her second so I don't know if that would have any bearing!
As for my scans, I had an early private scan that put my due date at five days later than the date I had worked out from LMP and cycle length but my "official" due date has always been that calculated using LMP and cycle length so I'm not sure whether that's because it matches the scans exactly or because, as it's not an exact science, the midwives and sonographers have just been working off the estimate 
The hospital I'm booked into do a 32 week growth scan as a matter of course and I have mine next week when I should be 32+6 so I think we'll wait until then to make a decision to see if there's any change in my EDD!
Doesn't help that until this came up I was operating under the misapprehension that it wasn't until 38 weeks that you were considered full term - not 37!!