Building in the British countryside is an activity fraught with problems. If you thought fracking had it bad, consider the hurdles a modern country house has to undergo, running the gauntlet of concerned neighbours, planning stipulations and national policy.

See more images of Downley House

Happily, the system can be made to work - if you can conjure up enough architectural originality and verve. These qualities have never been in short supply at the offices of Birds Portchmouth Russum Architects. The practice - set up in 1989 by Andrew Birds, Richard Portchmouth and Michael Russum following time in James Stirling and Michael Wilford's office - isn't well known outside architectural circles. Yet work has a unique formal inventiveness and a deft way of presentation.

Downley House is situated in the folds of England's South Downs, occupying the site of an existing ruin. From the outset, BPR saw the project as a classic country house, one that enjoyed 'an unfolding sequence of spaces and views, composed of simple geometric forms nestling within the landscape'. The house itself is a confection of pure geometry: of circles, squares, grids and ovals, cut into a flowing landscaped garden and set against the ruined walls of the original house, 'a romantic verdant folly' that now brackets an external courtyard.

The circular arrival court leads into a tubular entrance hall that acts as a spine for the project and incorporates a dining room dubbed the 'foudre', or wine barrel. Circular staircases, roof terraces, concave walls and changing levels make for a complex interior plan, one in which the contours of the land are fully exploited in terms of views.

Craftsmanship was of the highest priority, from the carpentry down to the smallest fittings, while the mix of materials is sharply delineated, from the circular masonry wall surrounding the entrance to the gridded-oak pergola.

Twin wings - a guest space and the main living areas - unfold from the entrance hall, allowing each part of the house to act independently of the others. Glass and timber are used extensively, accentuating the curves of the structure and revealing views out, down and across the house, while a 'green' route winds around the indoor spaces and into the garden beyond.

BPR undertook careful consultations to get required permissions - this part of the country is designated an Area of Outstanding Natural Beauty, usually the death knell for contemporary architecture. A three-year planning process culminated in success, and construction of the house, using vast prefabricated elements, took just under two years from breaking ground to final snagging.