Check this link Frank you have most of the information you need on this.
www.ukspeedtraps.co.uk I guess this is really a question of bitting the bullet for that one.
You could try and contest saying that he measured the speed at quite a distance and because of the proximity of the Audi that was just overtaking you there could be some misreading. But you would have to contest on the spot and not accept guilt.
Also the laser equipment they use is very accurate and at that distance in a car you don't stand much chance. It would be a bit different on the bike because of the reduced size of the bike's front end and the difficulty for their equipment to get a reading on something that is all curved at the front end, they generally catch you at a closer distance with a bike (like 150m). That gives a little bit more of a chance to spot them.
But on the other hand, if you had been on the bike the Audi driver wouldn't have stood a chance hey, and you would have been done much faster!