chedgrave church

this church is a norman oddity, with this early c12 tower to the north of the chancel, with their east walls flush . pevsner says that there is a piscina in the tower , but does not give a date, and a door in its south wall. could this be a tower church to which was later added a more normal nave, or was there a problem with the foundations preventing any other than this position? its uniqueness has been buried under a north aisle of c.1820, and is further hidden by the most egregious and unsympathetic modern addition , which looks like a red brick medical centre, noy a church.