Neighbours large raised summerhouse overlooking our garden

[ShakespearesSisters]

After advice, I've googled and cant find the answer and wondered if anyone can help.
A few weeks back next door but one neighbours has a large decked, insulated and weatherproofed area built in their garden. The garden slopes up from the house and from one side to the other. From my garden my best estimate is this platform is 8mx4m. To level it, the one side is probably 50cm above ground level and the other end 1m above.
Yesterday walls started going up, just framing at the moment but that looks to be 2m, and the open side that I guess will be windows and veranda are facing directly onto our patio rather than orientated to look down their garden towards their house. (The garden between us is a student let with nothing but a lawn)
Does this sound like its outside permitted development?

The top of the garden where they have built is probably 1m above the ground level at the house.
The whole street is on a slope so all buildings at end of gardens will be up higher than house ground level but they are all green houses and sheds and look down the individuals garden.
I'm not so sure if I would have an issue if it wasnt for the orientation so it looks over our garden rather than theirs.
Sorry for the waffle.

Anything over 30cm in height off the ground needs planning. It is complicated by a slope so call the council. Our garden slopes away and we needed planning for our patio.

Permitted Development still doesn’t mean you can ‘just build it’, it means the permission process is less onerous. It can however be declined and full planning required - as happened to our neighbour.

Yes this doesn't sound right. Call the council ASAP so they can come around and take a look. I'd be surprised if they get the go ahead if it is as overlooking as you've described as it would have a detrimental effect on your privacy and amenity.

Thanks. The builders have just turned up so im guessing construction further today.
Just wondered if i was being petty or not. Doesnt sound like it.

Have you checked the council web site to see if they have planning permission?

Is it close to any boundary? If any of the building(shed/summerhouse) is within 2m of the boundary then it needs to be under 2.5m in height otherwise they need planning permission.

Permitted development does mean they can just build it, as long as it is within the rules.
Check the planning portal for outbuildings, and read the technical guidance document. If within 2m of a boundary it can only be 2.5 metres high. That though is measured from ground level, and if a slope from the highest point.

If they've put in raised decking to then build on top it'll probably be over height so call local planning to request they inspect.

Ring the council now!!

I rang, need to email them so I've just fired one off. Will see what they say.