I've had a lil look online, but I'm a lil bit stuck trying to find a suitable laptop for £500. I have a couple friends who are just finishing their architecture courses, but one of them uses a £1200 computer (similar to the £1400 monster I built for my brother's computer game design and animation course) with 3 monitors and the other has a couple specially built laptops that cost well over £1600 each (his parents bought one for him, and that was a tablet laptop).
As mentioned, modelling programs like AutoCAD are one of the more intensive applications a computer can be subjected to. My brother uses 3D Studio Max for his animation, which uses modelling, texturing and animation on top of it, most of which uses pure graphics card power (if I remember, it's measured in FLOPS, and my brother's HD4870X2 went up to 2.4TeraFLOPS). Whilst you can afford to use a mid-ranged graphics card to keep to a budget, it just means that everything will be that much slower. I also doubt that you'll be able to get much done with a low-ranged graphics card, such as the ones you find in the £300-500 range laptops.
Maybe I'm wrong and someone will find a good laptop in that range, but I believe you need a high end graphics card and plenty of RAM to work efficiently, which laptops generally can't offer until you're ready to spend over £1000 on it.