According to Maurice Craig's still-definitive Dublin 1660-1860, during the closing years of the 18th century the capital had a resident population of around 100 peers. Many of their properties, such as Leinster House, Powerscourt House, Charlemont House and Belvedere House, are still extant and well-known. Others such as Moira House have been destroyed or else, like Tyrone House or Aldborough House, have undergone such radical alteration in their use and appearance that it is difficult to imagine they were once private homes.

But there is another group of buildings developed for members of the ruling order which has survived relatively intact, often because they are less ostentatious than many of their counterparts. They are fronted in brick, rather than stone, and form part of a terrace, although each unit may have been developed independent of the others. This is the case with two very large houses in Ely Place which have just been refurbished to serve as the headquarters of the Ogilvy & Mather group.

Ely Place was developed in the very early 1770s, after Hume Street had been opened up as an access route from St Stephen's Green. Like so much of Dublin's growth during the 18th century, the development was speculative, with individual lots being sold off and then built upon. For this reason, there is relatively little stylistic unity in the street and the size of houses varies considerably. The largest of the sites is still occupied by Ely House, from which the street takes its name and which was originally seven bays wide until divided into two units in 1811. Next to it is number six and this, together with its neighbour, is now occupied by Ogilvy & Mather.

The company's executive chairman Mike Welsford says the reason for the move was to unite all the different divisions of the business - including Wilson Hartnell Public Relations - under a single roof. Previously the staff were spread over two sites in Appian Way and Leeson Park and operating in what had become cramped conditions. Running to some 18,000 square feet between the two houses, the new accommodation is not only 3 - 4,000 square feet bigger than the old but also lighter and, thanks to a complete fit-out prior to the move, far more suited to the workforce's needs. More than 140 members of staff have now moved into their new offices. While Mr Welsford declines to say how much the fit-out cost the company, he says the sum runs to six figures.

While not as big as Ely House, number six is still an impressively substantial building, in keeping with the grandiose aspirations of an early owner, John Fitzgibbon, first Earl of Clare, who bought the property from the Rev Thomas Carr and David La Touche in 1781. Although number six was already spacious, it was still insufficient for the owner's needs and he therefore extended the house at the back, primarily to include a new staircase and a banqueting hall or ballroom. Both still exist and are by far the biggest spaces in the building, the cantilevered double staircase with limestone treads rising up to a first-floor balcony that runs along one wall of the house and takes visitors from the former drawingroom to what was once Fitzgibbon's coved-ceiling bed and dressingrooms. Beneath these is an enormous chamber, alcoved at one end - presumably to hold a small band of musicians - and with its panelled walls covered in stretched canvas in order to improve the acoustic quality of the room.

Smaller than its neighbour, number five was built by Gustavus Hume around 1774 and two years later occupied by John La Touche, younger brother of one of number six's original co-owners. Almost 20 years later, La Touche let the building to Edmund Henry Pery, later Earl of Limerick and then, in 1806 number six became home to the Rt Hon Charles Kendal Bushe, Lord Chief Justice of the King's Bench of whom Henry Grattan is reported to have said, "he spoke with the lips of an angel." In the middle of the 19th century, both houses - like so many of their ilk - became government offices and remained such until the 1990s.

During the past year, they have undergone refurbishment by their owner, Pierce Maloney, who is currently constructing a block of apartments to the rear on a site which would have originally been occupied by the houses' gardens and mews buildings. A double-storey car-park has been inserted in the courtyard separating the apartments from the older properties, with 20 places allocated to Ogilvy & Mather.

Walking around number five and six, it is fascinating to observe the similarities between the two despite their disparity in size. The cornicing in the entrance halls of both, for example, is identical and the same stucco roundel depicting the Judgement of Paris appears above the diningroom in each house, indicating that the decoration of these properties came primarily from pattern books of the period. Similarly, the roundel in the groundfloor frontroom of number five is identical to that in the diningroom of Ely House.

The plasterwork in the pair of buildings occupied by Ogilvy & Mather is very fine throughout, although it is disappointing that during the recent restoration no effort was made to remove the accretions of more than two centuries.

As a result, much of the fine detail on ceilings and walls remains clogged with layers of paint and incapable of being properly appreciated. This is especially regretable because so few houses of equal quality are extant and on view to the public.

As well as ceilings bedecked with fine arabesques and human profiles, many walls carry ovals depicting ancient gods and goddesses. The stairwell of number six has walls carrying festoons of oak leaves, a motif which also occurs elsewhere in this building.

The stairs were originally top-lit by a glazed lantern and it is again a shame that during refurbishment work the opportunity to reinstate this feature was not taken. The limestone flags of the hallways have been retained, with some par ts needing to be replaced in the same material.

Similarly, wherever old wooden floors were capable of salvaging, they remain in situ but large sections of both properties are now carpeted. A lift shaft could not be inserted into the old buildings and has therefore been constructed at the rear of number six, with access to it on the upper floors achieved by a new glazed corridor placed on top of Fitzgibbon's extension.

Within each house, the first-floor drawingrooms are especially beautiful thanks not just to their plasterwork but also their generous proportions, marble fireplaces and line of long windows. One of the most visible interventions by Ogilvy & Mather and their architects, Douglas Wallace, takes place in the former drawingroom of number five where a metal-frame mezzanine has been placed in the centre of the space. While this does not interfere with the structure of the original room, it disrupts the latter's character, in part because the frame has been painted bright purple which tends to bleach out everything else.

Most of the rooms are white, although there are outbursts of yellow and orange used for walls on the former servant staircases and for staff coffee docks.

Mike Welsford says the intention of Ogilvy & Mather was to respect the integrity of the 18th century architecture "but counterpoint it against the company image we want to project: contemporary, youthful, fun - that was our brief to the architect." So an internet cafe has been installed in the broad vaulted passage leading from number six's entrance hall to the main staircase, and light fittings throughout are contemporary.

The largest amount of work has been carried out in the old basements which once housed various offices including kitchens. The basement in number five has been transformed into a staff bar which will eventually open onto a courtyard. The adjacent room has become a diningroom and also accommodated on this lower level are lavatories, showers, storage spaces and an IT department; the old coal holes beneath the road now house all utilities.

Ogilvy & Mather's new offices prove that it is possible to house a large business in an old property without disrupting the integrity of the structure or introducing a myriad of internal divisions. Five and six Ely Place are wonderful spacious buildings carefully adapted to a purpose quite different from that originally intended.

The only pity is that much of their inherent beauty still remains hidden beneath old paint and that a complete restoration has yet to occur.