My 2 year old lab has suddenly started pooing indoors during night. Previously had no problems with house training, he has had no changes in food or routine - has anyone any idea why this is happening & what I can do to stop it?

Firstly trip to vet to make sure he's ok in all ways. Then a really closeup look at his routine are you sure it's not been disturbed in some way? Has someone has a change of shift patterns even a neighbour suddenly changing routine can upset some dogs to begin with. Are foxes suddenly appearing nearby as these guys seem tocauseno end of trouble at times in Manchester even in built up areas,they bark and mark turf etc.

Make sure to clean up really well to prevent smells attracting him back and doing it out of habit and maybe consider going back to crate training for a short time in case a one off accident has set up a bad habit.

Gut feeling would be a recent upset tummy or routine has changed in some way somehow. Also check the ingredients of your food as lots of manufacteurs switching to maize instead of rice and it bulks up faeces amount, you never know worth a quick read up. And scavenging with could alter habits as well.