An announcement from DEFRA has banned metaldehyde slug pellets from Spring 2020. Metaldehyde poses an unacceptable risk to birds and mammals, its role in reducing hedgehog, amphibian and bird populations, poisoned by consuming contaminated slugs or pellets, has been well documented. It is also toxic to pets.
Although not a factor in the decision making, the ban will also stop farmers from creating widespread pollution of rivers and freshwaters with these toxic pellets. Only those using permanent greenhouses will be permitted to continue using metaldehyde pellets (where birds cannot easily venture).
If you have to resort to slug pellets use those that contain ferric phosphate which will degrade harmlessly in the soil. Use them sparingly, only 4 or 5 pellets per plant, and only occasionally. Note however using this method means slugs will tend to go underground to die so there will be little evidence on the surface.
A number of alternative slug and snail barriers, from egg shells to hair, gypsum powder and copper tape are often suggested but only very wide and thick copper tape works. The thin products sold in garden centres doesn’t contain enough copper. A barrier of gypsum powder or chopped up young brambles also seems to do the job, but definitely not egg shells (unless you want to help snails make their own shells stronger by eating the egg shells, which might distract them from your plants).
Alternatively go hunting after dark using a torch to find them. Best of all, create a pond and encourage frogs and toads to do the eradication for you.