Larder fridge icing up.

You should check the door seal, as ours doesn't close precisely , unless really pushed hard - if it isn't closed properly it ices up as you have described. We had the engineer in 3 times when we first bought it, and we are still not totally happy with it, but apart from having a new kitchen , there's nothing much we can do , just check every time the door is completely closed.

The drainage needs cleaned very often , I shove a drinking straw down and wiggle it , sometimes means a bit of a puddle but a towel sops it up , debri can get lodged in the drain

Mine is integrated and does the same, it's about 8 years old. The regulation dial can sometimes get moved when delving about inside and I assumed this was the cause of mine?

I am guilty of sometimes leaving the door open, so that is something I can change. It is worse in hot weather.
I defrosted last week but an iceberg has already formed.

Is your fridge freezer absolutely level? I believe that can impact on temperature regulation.

Is it possible you're putting warm food into the fridge and causing excess moisture to build up? Or leaving the door open to long at any one time? I'm guilty of doing that.

If all else fails Neff have engineers who will call (at a cost!).

You could try the mats, might work!

We have a very good local chap who repairs electrical things, managed to sort out my oven (twice) and the washer/dryer, but when he came out to look at the fridge freezer (opposite problem to yours, fridge wasn't getting cold enough) sadly it was beyond economical repair.

Mine does that (also about 9 years old)
I just switch it off and defrost it every so often and am careful where I put the salad!

No, Phoenix, it is probably 10 years old. I am reluctant to replace it as integrated fridge/freezers are not cheap.

Is it still under warranty?