Thanks for the replies. I was in a rush to go to the shops and should have looked a little more closely at the distance. Pinching the finger and thumb together, squinting and guessing doesn't always work!
The idea of 6 hours just seemed so atypical of a 737 flight. As for aircraft at Lasham, I have seen, some years ago, 707, A300 757 etc going in and out of there. It can be a rude awakening when this almighty noise begins and a look out of the window shows something the size of a 707 just a couple of thousand feet above! Sadly, there doesn't seem to be as much traffic in and out of Lasham these days (even pre-Covid).