Thanks for your enquiry.
I am afraid that you have no input at all concerning the conversion.
Planning permission itself (for which neighbours do get notified and have the chance to object to) is not required for a conversion, and is only required if the party is extending their property.
What your neighbour would have required, however, is Building Regulations approval, which is consent from the Council as to how the work is to be conducted. So, when your neighbour said he had obtained Council's permission, he would have been talking about Building Regulations.
I am sorry this is not the answer you were looking for, but if I have answered your question, I would be grateful if you could leave positive feedback.
The other part of the question was does it effect the value of my property?
Thanks for your reply.
I wouldn't have thought for a minute that this conversion will affect the value of your property at all, you'll be glad to know- no extension/monstrosity is being built, and all it means is that you will have living accomodation on the other side of your garage wall, but this won't down value your own property.
I hope this helps.
My reason for my poor feedback on the first answer was due to the incomplete answer not the actual answer hence the Exellent on the second rating my thanks for your help
No worries! Many thanks!