Click on photos to enlarge. Notes in italics from Pevsner.

Up indeed, at the top of a valley within a mile of the crest of the downs, near Harting. Oddly enough, the view from the house is wide rather than deep, taking in nearly 180 degrees of the lower downs and stretching as far as the Isle of Wight.

Uppark was built c.1685-90 by William Talman, and its three main fronts have not been altered since. It is a copybook example of the Wren-style country house, moderate-sized brick with stone dressings, comfortable to look at and live in. In fact its parentage is Dutch, and it was brought to England after the Restoration by men like Hugh May; Talman may have been May's pupil.

The design has to be judged by the very highest standards, and by these it is good but not quite first class.  The main front faces S, its homeliness poignantly emphasised by the rough grass which covers the original formal terraces. It has nine bays, the centre quoined and pedimented, and the basic trouble is that these bays are a little too crowded, and their ornament a little parsimonious. It is essential that in a house depending on proportion, the proportion is exact, and if the ornament is going to be spare, it must be free from meanness. A look at the almost identical centre of Tadworth House, Surrey, (right hand picture) will bring out clearly the difference between the good and the excellent. ... Plain wings, again with slight but important defects in the proportion: bays three and seven have their windows too near the quoined centre, e.g. (But the same is true on Tadworth Court).
Whilst I see what Pevsner is saying, I do not share his feelings. I find Uppark at least as satisfying to look at, if not more so, even seeing virtue in what he considers as faults. The bunching of the windows towards the centre gives the facade a focus. Two different solutions, equally satisfying.

Mid C18 arms in the pediment; below, the first floor window is flanked by pinched scrolls and swags of fruit, the ground floor has a doorcase with open scrolled pediment supported on rich Corinthian demi-columns and between them a lintel packed with curly carving.

The W front is seven bays wide and plain, with markedly different spacing from the S front, which does not help; the E front is identical except for a plain doorcase with segmental pediment resting on brackets, of the type used by Wren at Winslow, Buckinghamshire.

The E facade was originally the entrance and was approached via two -two-storeyed offices. This was all changed after 1746, when the estate passed to the Fetherstonhaugh family; the two lodges were demolished and a matching pair of offices built to the l. and r. of the house on the N side. They are plain Palladian with a three-bay pedimented centre ... 

The entrance was then moved to the N side, and was elaborated by a Tuscan screen by Humphrey Repton in 1812 (presumably designed by one of his sons, giving their customary 'assistance in the architectural department'). Nothing has been altered since.

Since the above was written, there was a devastating fire in 1989. However, a remarkable restoration has taken place. The photographs are from 2006. Further details of the house and its history, including interior photographs, at the National Trust website.