It may seem hard to credit in the midst of a fractious debate about whether Dublin should have a high-rise future, but it is nonetheless true that An Bord Pleanala granted planning permission 15 years ago for an office tower of "up to 40 storeys" on the George's Quay site, opposite the Custom House.

That decision was recalled at the appeal board's recent oral hearing on eight appeals against Dublin Corporation's decision last October to sanction plans by the Cosgrave Property Group for another high-rise development at George's Quay.

Inevitably, much of the debate revolved around the issue of whether the form and uses of the sculpted glass towers designed by international architects Skidmore Owings and Merrill represent a better solution for the site than a 1991 offices-only scheme by Keane Murphy Duff, for which planning permission is still valid. This is also one of the main issues on which An Bord Pleanala will have to make a judgment - although not if one of the appellants, Cllr Ciaran Cuffe of the Green Party, has his way: he has proposed a motion calling on the City Council to exercise its power to revoke the board's 1991 planning decision on George's Quay.

Mr Cuffe argues that there has been a "material change in circumstances" - a requirement for exercising this little-used power - since the decision was made. The changes include the adoption of two city development plans (1991 and 1999) and the Docklands master plan (1997), plus the fact that the scheme was never completed.

Only two of the 10 office blocks envisaged in 1991 were actually built; these are located on the river frontage and occupied by Ulster Bank and Coopers and Lybrand. Seven blocks were to be built in a staggered cluster behind them, with the tallest tower rising to 65.6 metres, as well as a low-rise block on the Moss Street frontage.

The latest scheme also qualifies as a "skyscraper" development by Dublin's standards. Its tallest tower, an office block with retail at street level, would rise to 73.7 metres - or just over eight metres higher than KMD's tallest building and 14 metres higher than Liberty Hall. But the architectural treatment is as different as chalk and cheese.

Roger Duffy, the SOM partner in charge of the current project, characterised KMD's 1991 scheme as the "portals of darkness", because of its reflective glazing, by comparison with his own firm's "towers of light". "Do we build this passe scheme that has planning approval, or do we make a statement about this time," he asked.

Duffy, who is based in New York, said the 1999 scheme was about optimism and confidence and the creation of "something that is unique and timeless". The Georgians had expressed "a new vision that was unique and different from medieval Dublin" and there was no reason not to emulate them in the current economic boom.

HE criticised the 1991 scheme for its "fortress-like" impact, with no public site access, no pedestrian amenities and no residential content (apart from eight units already built). By comparison, his firm's scheme addressed the human issue of publicly-accessible space and accorded with planning policies to promote mixed uses in the city.

Mr Duffy also said he had been talking to James Turrell, the American artist "whose use of light as an artistic medium is unique". Having been involved in creating the Liss Ard "sky garden" near Skibbereen in Co Cork, he is now realising a vast "celestial light observatory" carved into a volcano on the edge of Arizona's Painted Desert.

The idea is that the clear-glazed towers at George's Quay would be dramatically lit at night-time, to give them a beacon-like quality on Dublin's skyline. But lit or not, the SOM architect said, it was clear that "something large" would be built on the site - either the scheme now proposed or the 1991 "portals of darkness".

The fact that the current proposal includes 166 large apartments with an average size of 120 sq m, as well as a covered shopping mall, showed that it was "outward-looking towards the community", according to the developers' planning consultant, Bernard McHugh, rather than overshadowing existing buildings.

Local residents remain unimpressed. They were well-represented at the four-day oral hearing and managed to get across their point of view because they had the status of appellants rather than mere observers. What amazed them was the first-name terms references by Mr Duffy to senior Dublin Corporation planning officials.

"It seemed to them that there had been a whole lot of meetings and discussions behind the scenes, from which they were excluded, and it made them feel like second-class citizens," Mr Cuffe said. Apart from sending in their objections, they had been given no other opportunity to express their views - until the oral hearing.

Michael Smith, chairman of the Dublin city branch of An Taisce, probed the differences of view between the chief planning officer, Pat McDonnell, who recommended that SOM's scheme be refused, and the city architect, Jim Barrett, who said it should be granted subject to the office tower being reduced from 100 to 80 metres.

After An Bord Pleanala requested an environmental impact statement on the scheme, the architects availed of an opportunity to redesign it, scaling down the tower by a further 6.3 metres as well as reconfiguring and refining the scheme as "a cluster of building forms that create a sculptural massing", as Mr Duffy put it.

Despite these changes, the Irish Georgian Society said it believed that the proposed development would "ruin forever the traditional skyline of Dublin and change the vital context of the city's 18th century buildings, such as the Custom House and Trinity College" - a point also made by An Taisce and other objectors.

As far as the local community is concerned, the design changes would do nothing to reduce the bulk and mass of what it regards as an alien imposition. The Dublin Docklands Development Authority also made it clear to the presiding inspector, Karl Kent, that the current proposal does not comply with its master plan for the area.

All of the objectors argued that it was premature because the corporation is only now in the process of commissioning a skyline study to identify those parts of Dublin that could "take" high buildings. But Mr McHugh said the 1991 scheme was also high-rise and it had taken Irish Life 20 years to assemble the George's Quay site.

Times have moved on, making the 1991 design look like something from another era - which, of course, it is. Even if An Bord Pleanala were to refuse planning permission for the SOM proposal, it seems improbable that Cosgraves would simply start building the KMD scheme without seeking to ameliorate its "portals of darkness".

Whatever is built on the site will transform this part of Dublin as well as the city's skyline. CIE also has plans to redevelop the adjoining DART station as a major hub, hopefully creating a place of real civic quality to supplant its ramshackle atmosphere; it is likely that this scheme will wrap around the corner of Tara Street.

All of the issues were teased out by the inspector, who is no doubt already writing his report for the appeals board. It is now "in the lap of the Gods", as one planner put it. The board, which recently turned down two major high-rise schemes in the Docklands area, must make its fateful decision on George's Quay by September 29th.