THE watchdog who cleared Glasgow Labour leader Gordon Matheson of misconduct in the George Square redesign debacle has refused to re-open his investigation despite claims from the architectural profession that he mishandled it.

Stuart Allan, Scotland's Public Standards Commissioner (PSC), last week rejected a plea from the Royal Incorporation of Architects in Scotland (RIAS) to re-examine the episode.

In a report to its members this weekend, the RIAS described the PSC's "failings" as "lamentably poor" and said it had asked SNP Local Government Minister Derek Mackay to look again at the legislation governing the role.

The refusal comes as new figures show just 2% of the complaints to the PSC over the last three years have ended in a guilty verdict.

The RIAS has now asked the watchdog that oversees the PSC, the Scottish Public Services Ombudsman, to look into Allan's handling of its original complaint against Matheson.

Ombudsman Jim Martin recently described the commissioner's organisation as "obstructive and unhelpful" and accused it of "severely hampering" an inquiry into how it had handled another council case.

The international contest to ­overhaul George Square ended in farce in January when, minutes after the judges chose a winning design, Matheson announced the project had been axed. He had vehemently opposed the winner.

The aborted contest, which was run by the RIAS, cost tax­payers £100,000 and the ­architects involved another £200,000. The RIAS subsequently complained to the PSC, alleging Matheson had broken the councillor's code of conduct by showing improper bias in a legally binding procurement exercise.

A council ­whistleblower, former lead architect Kerr Robertson, also accused Matheson of trying to rig the outcome through staff coercion.

Matheson strongly denied any wrongdoing. After a six-month investigation, he was cleared by the PSC on both counts.

The RIAS claims the PSC failed to interview key witnesses including Matheson's fellow judges; failed to cross-check evidence; and had been too willing to accept Matheson's evidence at face value.

Robertson also complained about the PSC's inquiry, accusing Allan of quibbling over process while "missing the point that there was an overt attempt to rig the contest".

By coincidence, Allan is to be quizzed by MSPs this week on his annual report for 2012/13.

Papers submitted to Holyrood's local government committee show that between 2010/11 and 2012/13, the PSC received 600 complaints, and just 12, or 2%, ended in a finding of a breach of code of conduct.

RIAS secretary Neil Baxter called the statistic shocking, and urged MSPs to consider whether it was credible that 98% of PSC complainers were mistaken or misguided.

The Ombudsman declined to comment.