Dog suddenly pooing in the house

[hairyclaireyfairy]

We have a black labrador who is 18 months old, toilet trained really well when we got him at 12 weeks.
All of a sudden he has been crapping at night in the house, he seems ok in himself. He is the most lovely dog and is my shadow!! He rarely gets left in the house alone for more than a couple of hours and has a decent walk in the morning then a shorter one at night.
Any possible ideas as why this is happening.
With thanks.

I'm no expert but firstly I'd ask if there had been any changes to the dog's lifestyle, environment or the household. Have you a new pet/changed his routine or sleeping place? Visitors? New baby? Etc etc

Failing that I'd consult a vet to rule out any physical problems.

I'm sure that far wiser advice will come along soon and hope you sort the issue out with ease.

Thanks Vallhala, it's good to have someone else to go through the possible reasons.
No major changes here. Same as usual.
Think I may give him a day or two then nip him to the vets and get their advice.