The Window Tax was a tax on the value of a property. The tax could be assessed without intruding on the house owner’s privacy by going inside.
As a consequence of the tax, people blocked up windows, and built houses with fewer windows. It was repealed in 1851. (Fewer windows were a health and safety problem.)
The blocked up Abingdon windows, pictured here, were probably not blocked up to avoid the Window Tax, unless you know better.
It could be that internal alterations made the windows no longer necessary.
It could be that the space inside is being used for storage or that privacy is needed.
They could be an architectural feature – for classical symmetry
If you know buildings, in Abingdon, where windows are blocked up to avoid the Window Tax then I will do a part 2.