Thanks everyone for replies. You are all right of course, the problem is down to dampness. Wonderful Peter the handyman ( who I got from NappyValley, thanks for the rec) is here today.  He took off the damp stained back of a kitchen unit to reveal an even worse bit of kitchen wall behind, plus … the slugs themselves!  like something out of a horror movie! Anyway I am getting the whole unit cut out, everything dried. And repainted with damp proof paint and then a new kitchen unit and crossing fingers.  Liked the bit about a “ bun in the oven” though it’s a bit late for that now!

We had them a few years back and it was down to a slow leak from a pipe near our water tank. Find the source of the leak and they will magically disappear! Good luck

I’ve occasionally had them when it’s been very wet, although as others have said, it usually originates from a damp problem. They hate strong smells, so if you sprinkle some peppermint or lavender oil where you’re seeing them they’re more likely to be put off.

Agree about the damp, friends of ours had the same and they came up through floorboards.

 

It maybe the wet weather. We had slugs trying to get into the house via the back door. We just put salt down and haven't seen any at the door but they are in the patio🙄
On a lighter note in my culture, slugs in your house means you may have a bun in the oven😅
Good luck!

You’ve probably got a bigger damp / moisture problem behind there , as snails love a damp area and stick around telling their friends to come visit! I’d somehow get access behind the units and I’m sure the problem will become apparent . Once you sort the damp the snails will be gone

Anyone had this problem and either know a DIY solution or used a pest control company who fixed the 
problem? For the last few months we have had slugs appear on the  kitchen floor for no apparent reason.  They only come out at night although occasionally we do see them in the daytime, both big ones and baby ones.  We thought they were coming from the garden through the cat flap ( is this possible!?) but recently I have a horrible feeling they may be living/ breeding at the back of kitchen
units, in the dark spaces behind the actual cupboard spaces.  We kill them with salt when we see them and my partner has bought a steamer that he has used inside the cupboards but we still see the telltale slug trains most mornings.  All food is locked away and everything kept clean of course but nothing seems to work. We only have this problem in the kitchen.  We put the food waste bins outside at night in case the slugs can smell the food waste. Any solutions welcome inc recommendations for pest control companies that folks might have used.