Witnesses to the marriage were Thomas and Hannah Hall.

I'm not 100% sure, but I believe that John Edward Knibbs (also recorded as a son of John and Susannah Knibbs of Deddington, Oxfordshire) and this John Knibbs were quite probably the same person. In all the census records between 1851 and 1871 it's listed that John Edward Knibbs was born in Deddington at around 1815. There is no record of a John Knibbs being born there in 1815, but the only John born at around that time was this John, the son of John Knibbs and his wife Susannah Perry. He was baptised on 11 July 1813.
For the time being, I have kept this original record of John Knibbs being married to Mary Ann Hall at Enstone, and have added John Edward Knibbs as a different person. However, I am beginning to reach the conclusion that John Knibbs and John Edward Knibbs are the same person, and that maybe the marriage to Ann Predey was a second marriage.......not yet sure. 
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We can see John and his wife living in the parish of Westcote Barton, Oxforfdshire at the time of the 1841 census:
John Knibbs 30 Saddler (born Oxfordshire)
Mary Knibbs 30 (born Oxfordshire)
William Knibbs 1 (born Oxfordshire)
Hannah Hall 25 Ind (born Oxfordshire)

I'm not sure who Hannah was but am guessing that it was quite possibly a sister of Mary.
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Sadly, John Knibbs and Mary Ann Hall seemed to disappear from Oxfordshire after 1841. It's interesting to note that the first child we can see being born to John Edward Knibbs and his wife Ann Predey was their son John Edward who was born in 1850, when John Edward would have been 36 years old.
So.......was this perhaps a second marriage for him? Did he and Mary Ann Hall move to Liverpool plerhaps? Did he become a widower and re-marry?

Ann Predey was quite a few years younger than John, so she couldn't have married until 1838 at the very earliest, when she would have reached the age of 16, so an earlier marriage to Mary Ann Hall is quite possible.