Had the exact same problem, OP. I got it removed after a very long slog with the Council’s Planning Enforcement Team, so I advise you get onto them straight away. Don’t bother tipping your neighbour off - they will either say, go on then, or they will lie to you to tell you they’ll adapt it to make it more private for you (ours did the latter) and you will feel obliged to give them time to make changes. You’ll then waste more time waiting for them and then he angrier when they’ve made no changes. You’ve already spoken to them and they’ve told you they have no intention of changing it. That’s what you tell the Council.
You will almost certainly need to quote legal chapter and verse to the Council (we didn’t in our initial complaint as we expected them to know the law in their area of expertise, and the case handler at the Council got it wrong and initially told the neighbours they could keep their illegal structure!), so I strongly advise that you set this out straight away in your complaint. Don’t give the Council any scope to get it wrong or waste your time. Do not be concerned with looking ‘nice’ to the Council or bad for complaining, just be factual, explain why it’s illegal and the effect it’s having on you.
The case handler at the Council couldn’t understand that the tree house was a type of ‘platform’ which, under law, cannot be higher than 30 cm. If the neighbour wants this, they will need to seek planning permission and it is unlikely that this would be granted. So I would advise you set it out from the start.
I would suggest something along the lines of:
‘Dear Council,
I wish to report an illegal platform which is interfering with my privacy and right to quiet enjoyment of my property. [Describe it, how high, how near your property, the lights and fact that there are adults and children looking in to your garden AND house. The effect this is having on your family’s privacy and mental health. Fact that you are concerned that should you wish to sell your property this would turn potential buyers off. Explain you approached your neighbour but they were very clear they had no intention of removing it].
‘As you will be aware, the Government’s ‘Permitted Development Rights for householders’ technical guidance (updated September 2019) provides guidance on the interpretation of Class E of the Town and Country Planning (General Permitted Development) (England) Order 2015 (“the Order”) as amended. This provides as follows:
“Class E sets out the rules on permitted development for buildings etc within the curtilage of the house (see page 7). A Building has the meaning set out in the ‘General Issues’ section of this document and includes any structure or erection (see page 6)…’’ Clearly, the neighbour’s tree house is a ‘Building’ for the purposes of the Order.
Class E restricts the height of raised platforms within Buildings:
“A raised platform is any platform with a height greater than 0.3 metres and will include roof terraces” (Page 29)
The Order gives a non-exhaustive list of examples of types of ‘platform’ but does not give it a rigid definition. Nor is platform defined in the Technical Guidance, or indeed the Interpretation Act 1978. Clearly, therefore, the intention is for ‘platform’ to be interpreted using the ordinary and natural definition of the word. The Oxford English Dictionary defines “platform” as “A surface of area on which something may stand, esp, a raised level surface”. One of the examples in the legislation is “decking” which is a platform stood on by individuals. My neighbour’s tree house is clearly a platform subject to the height restrictions in the Order.
Please can you deal with this as above. I would be grateful to be kept updated on progress’
Best of luck!