Now I'm even more mystified about what happened to this church. As said above, St Katherine's Parish Registers were apparently discontinued in 1912 but baptisms, marriages etc took place there long after that.
I have been browsing the Newspaper Archives and the only piece which appears to be of relevance is this one from the Northampton Mercury dated October 11th 1946 which reads:
"St Katharine's Church, Northampton built little over a century ago and capable of seating a thousand worshippers, which is to be demolished to make way for a borough was memorial of buildings of community interest grouped around a garden of rest"
There is also a photograph of the exterior.
No other explanation of the whys and wherefores of this planning decision. So what happened in the 30 odd years in between?
Alan