The singing of offensive songs at football matches has decreased since the introduction of the Offensive Behaviour Act, Police Scotland has claimed.

Assistant chief constable (ACC) Bernard Higgins made the claim as part of the force's written submission to Holyrood's justice committee, which is currently considering plans lodged by Labour MSP James Kelly to repeal the act.

The legislation came into force in 2012 and has been the subject of protests from both football fans and clubs.

A spokesman for one such group, Fans Against Criminalisation, described ACC Higgin's comments as "unsubstantiated" and went to argue Police Scotland have "no credibility left on the issue".

It outlaws the singing of songs which "a reasonable person would be likely to consider offensive" and which "would be likely to incite public disorder".

The law was passed by the then-SNP majority government but the party has since lost its grip over the Scottish Parliament.

A majority of MSPs were elected at the last election on manifestos which pledged to scrap the law.

"In our view there have been observable improvements in behaviour, particularly mass offensive singing," said ACC Higgins.

He continued: "It is difficult to know how much of this improvement can be attributed to the Act alone and the University of Stirling evaluation of the Act makes the point that the legislation was one of a number of initiatives which collectively resulted in improved responses from bodies such as the police and Crown Office and Procurator Fiscal Service."

In August, it emerged Celtic's top security official warned a Scottish Government minister that offensive singing had increased as "an act of defiance" against the law.

ACC Higgins also went on to warn that repealing the 2012 law could mean some people will avoid "charge and prosecution" as the behaviour was not previously illegal under pre-existing legislation.

Police Scotland say "offensive songs which make reference to proscribed organisations", such as the IRA and the UVF, may be legalised after the Act's repeal.

"Until police reports are submitted and prosecutions completed under alternative legislation, it is not possible to quantify what proportion of cases will fall outside the scope of alternative legislation," said ACC Higgins.

A Scottish Government spokesperson said: "Police Scotland routinely patrol senior football games in Scotland and have extensive experience of how the Act works in practice.

"Their comments that the repeal of the Act potentially 'would be interpreted by some people as a lifting of restrictions on their behaviour' echoes concerns raised by representatives of victims and equalities campaigners and should be taken extremely seriously."

In response, Kelly said:"There are contradicting views about the success of the Football Act in reducing inappropriate singing at games and influencing fans' behaviour.

"However, human rights organisations have repeatedly raised concerns about the singling out of football fans, while legal experts like the Law Society have made clear that existing legislation is sufficient in order to combat offensive behaviour."

A spokesman for Fans Against Criminalisation said: "The relationship between fans and the police has been corrupted by this legislation and the way in which it has been actioned.

"ACC Bernard Higgins may wish to seek amendments to the law as opposed to repeal now, but repeal is all that will suffice if this relationship is to be mended."

If Kelly's bid to scrap the law successfully passes through the Scottish Parliament it will be the first time the devolved body has scrapped legislation previously passed by the institution.