OK, so this is a strange question...

I flew SFO to LHR on Thur / Fri on an overnight flight and according to the Imap we flew just north of the dark side (night side) of the world, the part of the world that the sun doesnt shine on at night. We were treated to some realy spectecular 'sun sets' as we flew over northern Canada and on to Greenland...

Ok, so this is where i am confused.. At 37,000 ft, was i seeing the sun shining on the 'other' side of the world (over the North pole), thats why the sun was on the left of the aircraft when flying West to East?

Give me more details. Flight number and time of departure.

Flight number or route doesn't matter all that much.

First off, you weren't really flying west to east. It looks that way on a 2-dimensional map, but you are really flying mostly north then mostly south.

Also, if you happen to be sitting on the north pole, you will see the sun shining from March 21 until Spetember 21, 24 hours a day (assuming no clouds of course). As the calendar approaches the summer soltice on June 21, the area where the sun shines 24 hours/day gets closer and closer to the Arctic Circle. So, at this time of year, it doesn't really matter which side of the pole you're on, it's going to be sunny all the time. (And at the north pole, the sun sets in the south and rises in the south.)

Simply put, for a "north american night flight going east" you will see the sun that is shining on the "other side" of the world on the left side, over the pole.

But then again the world is flat, just like the airshow map.

The flight was Virgin V020 from SFO, leaving at 4.30pm US time and arriving at LHR some 9 hours and 40 minutes later. I saw the sun setting somewhere over the far north of Canada and on over Greenland, so the Imap on board was telling me. It also showed that we were just outside of the 'dark side' of the earth (to its north).
Seeing the sun setting on the left hand side of the aircraft was quite confusing till i realised that flying West to East at such high altitudes and latitudes, i could see what was in fact the sun that was shining on the other side of the world, over the north pole, was quite a revelation!...

Thanks for those that confirmed what i saw. Is this possible on other routes, in the southern hemisphere i wonder?

I thought maybe the plane was just flying upside down...