The C11 nave has a mostly C14 oblong, gabled tower on a base that is probably earlier.  The chancel is C13 and C14.  The monuments range from then to the C20.

West Dean is in a long wooded valley running into the Downs from the Cuckmere.  A C13 rectory by the church, which was tenanted by two labourers in 1850 (3 p13), is now in something like its original state.  Unlike the C14 parsonage at Alfriston, it is flint-built with trefoiled windows.  Since 1528, the parish has been united with Exceat (VCH 2 p158).  The church there was in ruins by 1460 and its foundations, now marked by a stone, were uncovered in the early C20.  They were interpreted as a C11 apsidal church with a later porch.

West Dean church is also C11 in origin, as one north window in the aisleless nave, its head formed from one stone, shows.  The west tower is as broad as the nave, but shorter from east to west, making it oblong in plan.  The upper part is C14 (see below), but the line of an earlier gable suggests it was built on a C11 or C12 west extension, though Clarke and Leach prefer a C13 date (2 p106) despite most such extensions being of earlier date.  The flintwork is largely renewed, but the two-cell structure of nave and extension, which would probably have then lacked a tower, could be pre-Conquest.  However, the relatively broad proportions argue against this and though the round-headed arch between tower and nave has been altered, it was plain and looks C12 in origin.

Whether this first structure had a chancel is not known.  The present one is as wide as the nave and the oldest feature visible is an early C13 north lancet with no scoinson.  There is no chancel arch, so the roof is continuous.  In the early C14, the tower arch was altered with triple shaft responds on high square bases, all sharing a capital.  Conical corbels support the innermost order of the mouldings on the unaltered head.  The change may have followed a decision to build a tower above the western part, using more carefully shaped flints.  The renewed segmental west window with panelled tracery and the moulded doorway look C15, but the trefoiled opening above and pairs of smaller square-headed east and west ones are consistent with the C14.  The appearance of the spire is determined by the oblong plan, with truncated east and west gables.

The remaining chancel windows are early C14.  The three-light east one has cusped intersecting tracery and a moulded string-course under the interior sill.  Though renewed, an engraving of 1850 (3 opp p16) shows it unchanged.  The two-light side-windows have trefoiled lights – that to the north is blocked.  The C14 work was probably connected with two tombs (see below); one may commemorate Isabella Heringod, who died in c1329 (4).  The nave was also altered, with a broad trefoiled window east of the porch.  It is renewed and, in addition, the Sharpe Collection drawing (probably 1804) appears to show a pointed not a round-headed arch.  

Presumed C15 work is confined to the west doorway and window of the tower and also to a rood-stair at the north east corner of the nave.  Its lower entrance is now hidden by the pulpit (Langdon p263); at least part of the screen lasted until the 1840s (3 p16). 

In 1850 the stonework of the church is said to have been ‘in perfect preservation’ (ibid p18) and, if so, it is surprising that it was so thoroughly replaced at H E Rumble’s restoration in 1878 (WSRO Ep II/27/123).  Though his work usually repeated what had been there, Rumble was notoriously insensitive to old fabric and he also replaced the roof and most fittings.  The reported cost of the restoration, some £1233 (KD 1899), seems on the low side, given the amount of work that was done.  The two-light north nave window is C19 and it is not known if it had a predecessor.

Fittings and monuments

Bracket: (North chancel) Moulded and between tombs, with which it is probably connected, so it is early C14.
Font: C13 square bowl with a chamfered underside into which the capitals of the four supporting octagonal shafts are carved.  It resembles that at Alfriston.
Glass:
1. (East window) J Powell and Sons, designed by H Holiday, 1889.  This was altered or replaced in 1890 (Hadley).
2. (South chancel, second window) J Powell and Sons, 1917 (CDG 286 p126).
Monuments:
1. (North west chancel) Early C14 with a roll-moulded arch, a plain gable and finial.
2. (North east chancel) Possibly to Isabella Heringod (see above).  This is a little later, with a coarsely cusped arch, heavy side-pinnacles and a crocketed gable.
3. (North chancel) Susannah Tirrey (d1637) An early example of the cherubs and symbols of death that became popular in the later C17.  Since she was daughter of William Thomas (see immediately below), it is likely that this is also London work, though the quality of workmanship seems lower.   
4. (South chancel) William Thomas (d1639) and his wife (d1625).  A large monument, almost certainly London work.  Two large figures kneel within columns with two angels, beneath a rounded, broken pediment.  Llewellyn (p379) suggests this may have been erected in the 1620s.
5. Sir Oswald Birley, painter (d1952) Conventional head by C Sheridan (BE p622).
6. (North west nave) Lord Waverley (d1958) An altogether more vigorous bust by Sir J Epstein with a lengthy inscription, commemorating the former Sir John Anderson, Home Secretary in World War II, after whom the Anderson shelter was named.
Piscina: (South chancel) C14, with a fluted bowl and moulded sides but no head.  This may be missing because, according to Hussey (p219), the piscina was intersected by a window, though it is not now apparent what form this took.
Reredos: The Ten Commandments etc in iron; they do not look earlier than the C19.
Stoup: (by south doorway) C14 with an ogee head.

Sources

1.  W Budgen: Excete and its Parish Church, SAC 58 (1916) pp138-70
2.  H Clarke and P E Leach: The Medieval Churches of the Cuckmere Valley, SAC 123 (1985) pp95-108
3.  G M Cooper: On an Ancient Rectory-House in the Parish of West Dean with some Remarks on the Church, SAC 3 (1850) pp13-22
4.  W H Godfrey: All Saints, West Dean, SNQ 4 (Nov 1933) p236-37
5.  W H Legge: Villages and Churches of the Hundred of Willingdon, Rel 7 (1901) pp1-10

Plans
1. Measured plan of Exceat church, derived from excavations, in 2 p98
2. Measured plan by W H Godfrey and E F Harvey in 4 p237
3. Measured plan of West Dean church in 2 p105

My thanks to Nick Wiseman for making all these photographs available