Thanks Ammonite, that is an interesting website.
It does though, list the architect as Joseph Mitchell and the building as 1841-1866. I am fairly positive (if that is not an oxymoron) that it was William Smith and that work started in 1719 (after St Alkmund's had been completed). He died in 1724 before the church was fully completed.
There was later work carried out in the mid-nineteenth century, including the insertion of stained glass windows (which I am waiting for a sunny day to photo from the inside) and extension to the apse completed in 1865/66 (which can be seen in the photo) which probably accounts for the confused records.
It is still strange to think of many churches of the same design around the country. The thing I have always liked about churches is their uniqueness.

Kevin