@fizzypop100
The spare room is packed full of his clutter
Start to load it in the car and say its going to the tip and that you and your son will be spending time in there to ensure you are out of his way.
If he starts to complain, you make the point that he can have either the living room or the spare room as his own personal space but not both.
I feel your pain, DH has been a nightmare with this though he hasn't worked from home constantly in the past two years.
He's just got a new job which will be working from home 3 days a week. I've put my foot down and said that if this is a permenant arrangement I absoluetely will not tolerate the kitchen, garden, bedroom lounge, front room or DS's playroom again. He MUST use the spare bedroom and make it a permenant office as its grossly unfair and impacting on the rest of the family.
There needs to be a clear line between home / work otherwise I think its damaging to family life. Having a door you close so work doesn't spill over into the family should be done whether you have a spare room available.
Shit excuses like its full of 'stuff' don't cut it.
I've just cleared it out today and I'm going to paint in there to make it a nice room for him to be in.