The first view of the interior from the west entrance reveals, more clearly than is seen from the outside, the basic cruciform plan of the building, and focuses naturally on the great altar at the crossing. At the same time one is aware of an unexpected spaciousness, only fully revealed since the reordering of the sanctuary.
The nave which is the main seating area for the congregation, is defined by two rows of plain circular columns set on octagonal bases and terminating in capitals from which spring particularly handsome moulded arches. Over these, at a high level, are the clerestory windows which light up the wooden roof. This hammerbeam roof, the pointed arches, the foliated carving of the capitals and the carved heads on the corbelstones supporting the roof are all typical features of the Gothic style.
The transepts, the other seating area, join the nave by means of a single arch on either side. These arches are much higher and wider than those in the nave and rest on larger multiple columns. Four of these columns at the crossing are in almost square formation and mark out the centre of the building, where the platform for the altar rises five steps above the level of the main floor.
The chancel behind the altar is defined by the smaller columns and arches of the side chapels and by the raised floor, which joins the place of the altar with that of the bishop’s chair or ‘cathedra’, in the apse. The simple ribbing of the roof in this area distinguishes it from the hammerbeam treatment in the nave.
The side aisles and four side chapels are considerably lower than the nave, transepts and chancel, an indication of their secondary role in the overall structure.
The Lady chapel projects from the north aisle, with the same kind of arch as those in the nave. The semi-octagonal apsidal form echoes, less laborately, that of the great eastern apse.
The organ gallery over the west door is supported by eight columns in polished red Aberdeen granite. Like the wooden porches inside the west doors, the gallery was added by Hague in the 1880’s and was not part of McCarthy’s original plan.