You can either go round the conservatory every evening and gather up all the slugs you can see and dump them in a bucket of salty water (wear gloves to do this) or use slug pellets. I take it you have plants in your conservatory which is what is bringing them in. Be careful if you use pellets and you have pets, don't use too many and hide them under something your pets won't be able to knock over.

If you've been having this trouble for years, unless your conservatory has garden soil with plants growing in it, or has had the same potted plants for years (which could mean they're breeding in the pots), that would indicate there's a hole or cracks at ground level or on the floor of the conservatory, maybe where it joins the walls - repairs to make it all sound would prevent incursion by slugs and any other creature which gains access that way. If you're not aware of any holes or fissures, have a close look around - there'll be some way they're getting in, even if its difficult to find, even if its just a gap under the door or the door frame. Otherwise, there is no way of eradicating them completely; you can exterminate some by regular use of slug treatments, but there'll always be more.

We get them on our hall carpet and I have no idea how the little dears get in. I've just accepted it as a fact of life...

We get them in the house too. We think they come in attached to the cats.

I wouldn't expect them to last very long in the house.

I've seen them in houses and they can get through the smallest of cracks around the doors as they flatten themselves. I had a desiccated one in the car once (I'd taken a load of garden cuttings to the recycling centre and it must have been an escapee).

Owdboggy tiny ones do come in on the cat but I think these must come under the door as Cammomile suggests.