Flat Conversion Allowance

[Solomillo]

I am looking at converting storage space above offices into five self contained flats. The building was built around 1915 and up to 1968 it was part used as a Police Station with Police Officer accommodation in an integral three storey house.

If I can use the Flat Conversion Allowance then the conversion costs can be set against my other income.

The property would seem to fit the criteria in the FCA manual from the Inland Revenue at http://www.inlandrevenue.gov.uk/specialist/flatsovershops.htm except that we do not know if it was originally built as a domestic dwelling.

The Inland Revenue say that "the upper floors must have been originally primarily for use as dwellings".

How would the IR decide whether or not this was the case and if FCA would be allowed?

Should I ask my local Tax Inspector before going ahead with the project or would that just create a problem that would not otherwise exist? After all, the property is in a residential street and, from the front, looks like a couple of large houses.

Thanks in advance for any guidance.