The church is on the Northway Estate, just inside Oxford's northern ring-road
Get to the roundabouts at the bottom of Headley Way: From the
northern part of Oxford's ring road (A40): between the roundabouts for
the A40 (east to London/M40) and the A4165 (Banbury Road) you will
find a turn-off for Marston and the John Radcliffe Hospital. Follow
those signs. and you will reach a pair of roundabouts via Marsh Lane,
with a BP Garage opposite. Turn left at the first roundabout, and go
straight ahead at the second (there is a row of shops on your left).
Now you are at the bottom of Headley Way.
Turn onto Northway Estate: turn into the road on the top side
of the shops (this is on the left, if you are following the directions
above); this is Copse Lane. Follow the road (it becomes Westlands
Drive) past some more shops, towards a tower block. Before that
block, turn left into Maltfield Road, then right into Sutton Road,
where you will find the church.
You may find it easier to use an interactive map provided by Google.