You pretty much nailed the panning part, and exposure seems ok even if a little bit underexposed. However composition/crop is too tight and, combined with the straight-on angle, effectively kills the sense of motion one expects to find in this type of photographs despite the presence of back-/foreground blur.
hee! i would have though it would be more of a challenge to find a car without the flag in the last week or so! from the wing mirror and the door handle and similar details, you can tell this is a sharp, well timed, well captured moving image; but it feels let down by the flappiness of the flag. i think this is where the motion blur requirement of the challenge doesn't quite fit the nature of the shot. it's a pity it wasn't a flag not saying england - i think the lack of text would make it appear less apparently flappy.
it's also let down a bit by the agressive crop of the cars nose and the tightness towards the rear. the only way round this would be to crop much closer to the flag. still, merit should be given in that it is a welcome non-conformist shot from the typical car panning picture, and the motion blur is caught in such a way that it gives a great impression of speed. 6.