The interior of the castle has seen many changes and it is now difficult to sort out the uses the rooms have had in the past and the dates when the changes have been made. The principal character is now of the mid-C18, modified, but in the same style, perhaps in the mid/late C19. It has been assumed that all the C19 alterations are of the same date, in fact that of the porch and therefore c1840-78, though this may not be the case.
The castle is currently entered through the Victorian porch directly onto the Stairhall via what previously may have been a window. RCAHMW say, however, that this was Colonel Jones main entrance in the 1660s (but see below). This room is clearly an amalgamation of two rooms on each floor but this seems to have been achieved at two periods, firstly when the stair was inserted into the southern half of the room and secondly when the two rooms to the north were included in it. This second change must have happened either in the late C18 or is partly a late C18 pastiche done in the mid/late C19, perhaps when the hall was made into the main entrance (if it was at that time). These changes can be explained in several ways, but the main puzzle is the bottom of the staircase which would need originally to have been turned at right angles at the bottom to fit within the south room.
In the 1760s the main entrance to the castle appears to have been through what is now a French door on the south elevation. This door is late C20 and was previously a sash window like the others so must have been changed when the main entrance was moved to the west courtyard. This entrance would appear minor for so important a house but it is known to have had the entrance drive aligned on it . There is also evidence of an entrance directly into the tower on the right in a sally-port position and this reaches the Stairhall from behind the staircase. The mid C18 doorway entered a lobby, now included in the main south room, but ceiled separately and intended to be an entrance hall. The rest of the south room, no doubt once entered by double doors, seems likely to have been the State Dining Room, despite being so far from the kitchen. It is the only room that could take advantage of the late afternoon sun and its position beside the front door would also have been convenient in use. After the Victorian alterations it became the Drawing Room and the room added beyond, through the panelled double doors (probably these were previously the doors from the entrance hall), was the Smoking Room. The main room has a simple late C18 plaster cornice and fireplace. There are pilasters at the join of the rooms and the former entrance hall has a panelled dado, additional Rococo decoration to the ceiling and a grand doorcase as entry to the Stairhall beyond.
The alterations in the 1760s were undertaken by Thomas Paty of Bristol and the plasterer Thomas Stocking; the Rococo work at the castle is very characteristic of him. The use and decoration of these next rooms in the period 1680-1760 appears to be largely unknown and yet this is vital to an understanding of the way the house worked and of the ideas used by Paty in the alterations. There must surely have been a staircase at this end of the house during this period, but was it in the same position as the current one?
The Stairhall contains an apparently late C18 staircase with two turned balusters per step, cut string with scrolled tread ends, a curtail and a moulded pine handrail. It climbs in two slightly awkward flights past a landing with an 8-panel door which gives entry to the south-east tower with its different floor levels. Similar door on the upper landing into the main south range. The stair enclosure has a Rococo ceiling and windows in the upper and lower west wall. The north end of the hall has a late C17 bolection moulded fireplace on the ground floor but there does not seem to have been a matching one in the wall above. The upper part of the room is entered through a flat headed break in the wall, framed by pilasters and the upper landing is carried on a cantilevered balcony with turned balusters and handrail as before. All this suggests that the northern end of the ground floor with the windows flanking the fireplace was the late C17 Dining Room and, after 1760, but before the present Stairhall was formed, would have been the Breakfast Room (it faces east) or the family Dining Room (it's much closer to the kitchen). The upper part of the room would have been a small Withdrawing Room, but it was apparently unheated so it must have been just an anteroom. The west facing windows are of C17 dimensions. The ceiling with cornice as before and central Rococo decoration, is higher than that over the stair.
Having progressed from dinner up the stairs and through the first apartment the largest and finest room is now reached. This is the Grand Drawing Room and Library running from east to west across the building and being lit by a Venetian window at either end, a stone one to the west and a timber oriel to the east. This room is mostly within the first floor hall of the first build tower but no evidence remains of what it might have been like before the 1760s. The room is divided into three sections with the largest in the centre. This is framed by extremely flattened segmental arches at either end, the east one being a break through the c1200 wall of the first build, the west one an invention of Paty's as a balancing device. The soffits of these arches are coffered with plaster flowers and with bearded heads as keyblocks; while the arches are supported on panelled pilasters. The main ceiling has trophies of the chase in the spandrels and arabesques and wreaths on the flat, with a central Apollo head in a sunburst. The gilt chimneypiece is copied from a plate in Thomas Johnson's 'Collection of Designs' published in 1758. Payments for work to this room were made to both Paty and Stocking in 1766-7. The west part of the room is further lit by two windows overlooking the entrance court on the south.
The south-west door from this room goes through to a private Library or Study, while the main door on the north side is onto the family stair and rooms in the late C17 north wing. This staircase rises only from the Drawing Room floor to the upper bedrooms. It is a late C18 open-well stair inserted into an existing space and in details the same as the main stair. Several of the larger rooms in the north wing have full height panelling and bolection moulded fireplaces characteristic of the late C17.
To return to the ground floor the service end of the house is entered at the north end of the Stairhall. The basement of the original build contains the Estate Office and a windowless room with a stone staircase rising through the wall into the C13 addition. The north wing has a spine corridor with the first room on the left a barrel-vaulted C16 'Cellar' with a large fireplace. This is likely to have been the main Kitchen in the C16 and C17 before the new Kitchen was built in the 1660s. This is beyond on the east side and contains good fittings of the early C18 (dresser) and Victorian period (cooking ranges).
At the head of the stair is a chamfered pointed arch of Sutton stone which could be C16, but the stair itself is believed to be C19. It is cut very clumsily through the medieval walls and has a rather uncertain marriage with the bedroom stair as if it is an afterthought. The stair continues as a mural stair up into the C13 tower while the arch leads to the bottom of the family stair described above. The mural stair is one of the few medieval castle features still visible internally. There is another stair in the south-east tower, there are several rooms at the top of the two towers with circular corbelled roofs (six in all), and two garderobes are visible with the probability of more. The first floor room in the south-east tower shows signs of having been worked on in the Victorian period; it has a 2-light window and walls dressed with blue lias; this may have been an unfinished intention as a 'medieval' boudoir.
The visible timber roofs are all C17 and of the principal rafter type, but with many repairs and alterations.
The developmental history of this interior remains unclear. Questions still unanswered concern the C17 staircase, the former nature of the rooms making up the present Stairhall, the uses of the rooms at different periods and the particularly vexed question of the main access to the house at different times, especially from 1660-1760. There is also the very confusing question of how much of the apparently C18 decoration and alterations may actually date to the C19.