TWO police officers are under investigation after being accused of lying on the stand in a case involving a football fan acquitted of his role in a notorious incident.

The chief inspector and sergeant facing the perjury probe had given evidence against a youth charged with breach of the peace for his role in the kettling of Celtic fans on Glasgow's Gallowgate in March 2013.

During the trial of Scott Johnson, one of the officers was warned by prosecutors that he was in danger of incriminating himself even though he was a Crown witness.

The pair were then the subject of a complaint to the Crown Office by a member of the public, leading to the investigation by the Police Investigations and Review Commissioner (PIRC) confirming a perjury investigation is underway.

It comes amid moves to take the case of two men found guilty under the Offensive Behaviour at Football Act to the UK Supreme Court.

Lawyers for William Donnelly and Martin Walsh are currently seeking advice from counsel on whether they have robust enough grounds to take the case to the Supreme Court.

The pair, both from Dumbarton, were charged with engaging in behaviour which was likely or would be likely to incite public disorder by singing a song in support of a proscribed terrorist organisation and given six-month football banning orders.

The "Roll of Honour" song commemorates Irish Republican hunger strikers from the Provisional IRA and INLA.

The pair appealed the decision on the grounds the law was unclear about the songs but this was refused in March.

But it has also emerged that evidence given by police in the initial conviction and cited in the refusal of their appeal is now being questioned, with one MSP seeking meetings with the Lord Advocate to discuss the matter.

During the trial officers had said Celtic and various supporters' clubs had warned fans of the undesirability and dangers in singing this particular song and that would have added to the pair being aware of the song was banned.

But documentation from Celtic and seen by The Herald disputes that they have ever publicly indicated the song was sectarian or otherwise. The club said it had had a meeting with the police where it was indicated fans would face potential arrest if singing roll of honour but the dates show this was a month after the Easter Road game leading to the conviction of Mr Walsh and Mr Donnelly.

Glasgow MSP Paul Martin said he was pursuing a meeting with the Lord Advocate as disputes over the quality of evidence in such cases were undermining confidence in the legal system.

He said: "The whole issue is about consistency in the presentation of evidence to the Crown. Given the significant public interest it isn't beyond the police to have some consistency in their records and accounts and to be held to account for it.

"And it is up to the Crown to ensure that is provided. Of course there is a police complaints process but what do they learn from this?"

A spokesman for the Police Investigations Review Commissioner (pirc) said: "The Crown Office and Procurator Fiscal Service has directed the Police Investigations and Review Commissioner to carry out an independent investigation into allegations that a police officer has committed an offence."

A Police Scotland spokeswoman said: "It is firmly established in law, and has been well publicised, that Police Scotland considers that singing songs of a sectarian nature or aligned to prescribed terrorist organisation at football matches is a criminal act under the Offensive Behaviour at Football and Threatening Communications (Scotland) Act 2012.

"The courts have stated 'there is no need for proof of knowledge that the particular supporter was aware of the law or the status of the song'."