I quote from "Oxford - an architectural guide" which does not provide a name for the church other than "Iffley Church" although I am certain that when I was there a sign did use a specific name. Anyway:
"...the most impressive piece of Romanesque architecture in Oxford, barring St Frideswide's Priory, is the parish church at Iffley..."
According to this book the church was built, possibly in the late 1170's. This makes it one of the oldest pieces of architecture in Oxford.