Any planning experts around - neighbour's summer house

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Hi

My neighbour is currently building a summer house/office at the end of their garden. It's a flat roof over 3m tall, less than 1m to 2 boundaries and approx 1.5m from ours; no fireproofing as far as we can tell, no planning permission.

They've also just started building what looks to be a wooden shed in the larger gap attached to the summer house on our side. It's also currently attached to our fence on the other! We've spoken to them and they've said the builder wasn't supposed to do that and that they'll ask him to change it today. However I don't believe they've any intention of leaving any gap between it and our fence.

Is there anything we can/should do, particularly bearing in mind that we're hoping to sell within the next few years?

Does anyone know if a summer house can form part of a boundary line and not have a fence in front of it?
All sizes of Summer house will comply with planning, under 2.5 meters high and under 30 m2 in floor space

@DAS123 the 30m2 is building regs, not planning.
There are a variety of different things other than height which means that PP may be required. Certainly if it is forming a party wall - so straddling the boundary, or if any part (roof, gutters etc) overhangs the boundary, full PP will be required. Permitted development rights only apply within the boundary (curtilage) of the property involved.

Thanks for your response, the summerhouse backs onto farmland, the farmer is asking me to put a fence in roof it but I’m saying the Summer house is my fence?