Yesterday the Glasgow-based practice officially unveiled its vision for the square which includes lighting schemes, a flowing water channel, Caithness stone surfacing and, controversially, a 'Goodnight Grassmarket' message beamed down on streets.
Local heritage watchdog, the Cockburn Association, confirmed it had 'serious concerns' about the plans. Director Moira Tasker likened the scheme to a 'bland and corporate' business park entrance.
However, Gillespies partner Brian Evans, insisted the design was 'founded on a considered understanding of historic spaces'.
'[It has] attracted critical acclaim nationally and internationally for the sensitive reinterpretation of public life in the contemporary city.'
Cllr Andrew Burns, Edinburgh City Council's executive member for transport and public realm, accepted that the scheme would not please everyone but insisted it was a sensitive treatment.
'I would refute that the proposals were met with a great deal of scepticism and concern. In fact elements of the scheme have received widespread backing from the local community,' he said.
'This project cannot though achieve everything that everyone wants. While some people are keen for public toilets to be returned to the area, other groups are against the idea.
'The proposals will improve existing lighting and any additional lighting will be sensitively addressed, and pedestrian priority is the centrepiece of the whole scheme.'
Gillespies plans to submit the scheme to Edinburgh's planners 'later in the summer'.