Slugs and snails have a lot of natural predators – including birds (especially thrushes for snails), frogs, ground beetles, hedgehogs and toads. So always do whatever you can to make your garden as friendly for these animals as possible and encourage them to deal with slugs and snails for you.
Go out in the evening on slug and snail patrols and hand pick any you see. Take them far away from your home (snails have a homing instinct, and will travel back to your garden otherwise) to get rid of them or kill them in hot water.
There is a biological control based on nematodes for slugs, but this doesn’t work on snails, called Nemaslug. This is watered onto the compost or soil from spring onwards.
You can place traps, such as scooped-out half oranges, grapefruits or melons, or jam jars part-filled with beer sunk into the soil, near vulnerable plants. Check them and empty them daily. Beer traps may also trap other animals, including ground beetles that eat slugs.
Place suitable barriers around susceptible plants. These include anything sharp and gritty including sharp sand, egg shells and cinders. Moisture-absorbent materials are available, which also prevent slug invasion, including Doff Slugs Be Gone and Vitax Slug Gone. Many barriers placed around plants on the soil won’t stop those slugs that live in the soil.
You can also use copper tape, especially around pots or raised beds, or use mats of Agralan Slug and Weed Mat or Slug and Snail Shocka, which is impregnated with copper. Copper produces a mild electric shock that deters them.