One of the great misfortunes of contemporary architecture in Ireland has been the paucity of patrons prepared to commission imaginative new work. It is a feature of the Irish psyche to be conservative, and this is particularly the case in relation to visual taste. The result is a preponderance of repetition, with once-fresh ideas driven to staleness.

A newly-refurbished city centre home serves to highlight this regrettable state of affairs because while the client is Irish, the city is London.

Michael Collins Cronin is a retired businessman and the son of Kitty Kiernan, the inamorata of Michael Collins; three years after his death in August 1922, she married Felix Cronin, but named her second son Michael Collins.

Now in his early 70s, he divides his time between homes in Dublin and London. The latter property is a small mews-like house built as one of a pair 30-odd years ago on a narrow lane in Knightsbridge. Although he bought the property in the late 1980s, Mr Cronin was content to leave its 600-odd sq ft interior untouched until a couple of years ago when a chance meeting with London-based architect Andrei Bowbelski caused a change of mind.

Bowbelski and James Davis are the principal designers at an English practice called Ziggurat which is not, its founders are keen to stress, advocates of minimalism; Bowbelski says his key influences are Palladio and Le Corbusier.

Entered through a narrow door, the space held a slender corridor with a bedroom at the front and a livingroom to the rear. Between these two were inserted a diminutive bathroom and kitchen, both lit by inserting windows in a roofline raised slightly higher than that of the rooms on either side. Little light entered the bedroom while the north-facing livingroom, although the best of the spaces, suffered from a considerable degree of gloominess. Beyond it was a narrow yard ending in a high wall shutting off all views of the neighbouring garden.

Michael Cronin's ambitions were two-fold: to increase the amount of space; and to encourage a greater sense of light and airiness inside the building without altering the front section of the property. The visitor still enters into a small corridor off which are sited a bedroom and bathroom. It is beyond the latter that all new work has taken place.

They chose to build down, excavating more than a metre below the old floorline to create a double-height space at the rear. More than 15 tonnes of soil were removed from the building, carried in bags through the front door.

Bowbelski is particularly pleased with the way in which the eye of visitors can be drawn from one space to the next along a diagonal line, thanks to the introduction of a sequence of gentle curves.

The old corridor, now floored in beech, leads to a short flight of steps leading down at a diagonal angle to the new living space. Thanks to the drop, under the original bathroom a new kitchen has been tucked inside what is effectively a large cupboard; there are even storage units fitted on to the kitchen door which, when this is closed, neatly fill the central galley.

In the living room, the same economical use of space is apparent in a circular work desk fitted neatly under the upper rungs of a second flight of stairs leading to the new bedroom deck; the area beneath these stairs also has a section cut out to accommodate Michael Cronin's television and video player. Next to this is a seemingly solid wall, the lower part of which holds a pane of opaque glass beneath which rests a dining table.

In fact, this table, and indeed the entire wall, can be pushed to one side in order to gain access to the reordered backyard; the division between interior and exterior thus appears to dissolve. The north wall has been given a concrete bench. The entire yard is painted white except for the upper west wall which is now a bold red - ideal for catching the evening sun.

Colour has also been introduced inside in an equally dramatic fashion as the new south wall that acts as a screen to the upper bedroom is painted aqua green.

In addition to a rooflight, the bedroom benefits from the northern window thanks to two substantial cut-out sections of the screen. Within the room itself, cupboard doors are painted grey and these slide back to reveal plentiful storage and a second bathroom.

The entire job took 18 months and while the initial budget of £50,000 (63,486) was exceeded, both Cronin and Bowbelski agree this figure was rather unrealistic given the nature of the task.

Now that work has concluded, Cronin professes himself delighted with the outcome, having, he says, always wanted the opportunity to make a bold aesthetic statement.