Property within Curtilage of Listed Building

[coles101]

I am looking for some help / guidance on the classification of properties within the curtilage of listed buildings.
I have recently applied for planning permission to my council to change the existing timber single glazed windows to new UPVC double glazed units. I was told that as it was a material change I would need to make a formal application but if I kept them timber I did not need to notify them.
After I submitted the application the council came back to me telling me that the property was listed and I would need to make a Listed Building Consent application, I challenged this as I knew the property was built in 1987. They eventually agreed that the property was not listed but as the building next to mine was listed the application would be qualified as “property within the curtilage of a listed building”. My application was rejected under the grounds that the replacement windows would be detrimental to the setting of the listed building as UPVC profiles cannot be produced to match the existing timber ones.
As a quantity surveyor who has worked in the construction industry for over 10 years I appealed to the planning inspectorate on the grounds that a UPVC profile could be produced to match the existing, I also provided them with evidence that it could be done, but the appeal was dismissed for the same reason.
My understanding of the Planning (Listed Buildings and Conservation Areas) Act 1990 is that a building can only be classed as within the curtilage of a Listed Building if it had been there since before July 1948. Is this the case or have I misunderstood?
I bought my house last September just after HIPs where abolished, however as the property was on the market for a while a HIP had been completed. The Property Information Questionnaire contained in the HIP stated that the property was not listed nor contained within a listed building. Also my solicitor did not notify me that the property was on the council’s records as listed.
As far as I can see I have two options:
Challenge the Appeal Decision on the grounds that my property has incorrectly been assessed as listed.
Take action against my solicitor / the vendor for providing false information when I purchased the property.