Cooool What do you do to encourage them - we have lots of food for them .
Put an old sack on the ground and water it occasionally. That will encourage the slugs. The slow worms will soon find them and will be glad of the sack to hide under while they munch on the slugs.
If you have a compost heap, they'll often shack up in there.
Also put down something for them to bask under - a small sheet of metal or black tile, something that warms up in the sun. Slow worms are protected under Schedule 5 of the Wildlife and Countryside Act, so if you can encourage them it might help slow down the decrease in numbers.
They're lizards, so if you do find a living one that a cat has brought in be careful how you pick it up. They shed their tails to deter predators so you could end up with a handful of tail, no slow worm, and lots of blood!