I've towed them down, I remember a couple of years back up here they used to deduct off your total £5 quid for each tire you left with the scrap car!!!
If you can be arsed... cut the cats off, were getting £75 quid for a original cat, its worth saving scrap batteries aswell if your scrapping lots of cars...
I bought a 2 litre Mondeo last year just for the engine ( to go in the Orion / zetec turbo ) Payed £125 quid for the car. Had engine out, plus other bits and bobs, it weighed in at £90 quid, & I got £50 quid for the cat = Free engine plus other partsand I was in profit just...