The Scottish Palestine Solidarity Campaign has launched a blistering attack on the sheriff who found a student guilty of racially abusing a Jewish postgraduate in his university hall of residence.

The anti-Zionist group said Sheriff Charles Macnair had "violated every canon of fairness and balance" in finding Paul Donnachie guilty of the attack on Chanan Reitblat.

Donnachie rubbed his genitals before wiping his hands on an Israeli flag pinned to Mr Reitblat's bedroom wall. Moments later he shouted about "a nation built on terrorism".

He was expelled from St Andrews following the landmark judgment at Cupar Sheriff Court in Fife last week.

The SPSC was particularly angered by Sheriff Macnair's refusal to allow three "expert" witnesses to give evidence. In a statement the SPSC said: "Macnair dismissed the relevance of the legal precedent of the [Jerusalem String Quartet] trial…which distinguished between hostility to the state of Israel and racism, on the grounds that the 'offence' was racist because it took place in a 'private space' rather than in public.

Palestine Solidarity furious at conviction of Donnachie in St Andrews flag case

"The logic of Sheriff Macnair's ruling would be that criticism of the state of Israel will be inhibited on numerous occasions within earshot of Zionist Jewish supporters of Israeli ethnic cleansing and apartheid on the grounds that they are 'members of Israel'."

Dr Glynn, a teaching fellow at St Andrews, wrote to Fife's The Courier newspaper berating the verdict, which, she said, had "moved us a step closer to an Orwellian police state".

She wrote: "A national flag is a political symbol. Desecration of a flag is a long-established method of making a symbolic protest against a political regime.

"Paul Donnachie's protest was directed not against Chanan Reitblat as a person or as a Jew, but against the political position that he so clearly supported. It was not racist. The way that he chose to protest was hardly in very good taste, but that should not be a matter for the courts."

Donnachie is due to be sentenced on September 13. The SPSC called on "supporters of Palestinian rights, anti-racists, and supporters of free speech" to protest outside the court.

A page calling for "Justice for Paul Donnachie" on Facebook was initially bombarded with messages both backing and attacking the Blackpool-based 19-year-old after his conviction, but has now been shut down and deleted.

Mr Reitblat has said he felt a sense of duty to defend himself and see his abuser brought to justice.

The Lithuanian-born American said he realised the trial would become a landmark case, and that despite the personal hurt and humiliation, he must give evidence.

"This was not just about me. This was for every Jewish student who has felt afraid to express their identity," he said.

"I go home with my head held high and can go on with my life and my studies. I'm satisfied with the verdict and hope it will have a positive impact for Jewish students."

The 21-year-old said the trial had been "humiliating but cathartic," and paid tribute to the Jewish community in Scotland who supported him.

Mr Reitblat and members of the chaplaincy board, who had accompanied him throughout the trial, had to be escorted back to their car by police as the protesters shouted abuse after the verdict.

He said the protests had intimidated him and left him "deeply offended".

"The behaviour of those two groups clearly indicated to me that their motives are not so much to do with defending Palestinian rights as they are to do with the destruction of Israel."

I identified the so-called experts

On the second day of the trial , the defence moved to call - without prior notice - three expert witnesses: Mick Napier (Napier University, Edinburgh), Dr Sarah Glynn (Edinburgh & St Andrews Univ-ersity) and Liz Elkind (Edinburgh University).

The defence failed to inform the court that these so-called independent expert witnesses were respectively the chair of the Scottish Palestinian Solidarity Campaign (SPSC) and two leading members of the Scottish Jews for a Just Peace (for Palestine).

I wrote a note to the fiscal giving the backgrounds of these "expert witnesses," and as a matter of urgency summoned the court's bar officer to hand it to the prosecutor.

The court adjourned for lunch, but I met the fiscal before court resumed.

Brian Robertson, the prosecutor, thanked me for the information, of which he had had no previous knowledge. There was every indication that the defence lawyer had also not been briefed.

And so, when the first of the three witnesses were due to be called, the Crown objected to the entire line of evidence with which the defence intended to lead. The defence counsel now referred to Napier as the chair of SPSC and the sheriff soon dismissed any prospect of him or the other two being allowed to give evidence.

Paul Morron is a member of the Northern Region Chaplaincy Board