POLICE have warned Celtic supporters attending a rally against Scotland's football laws that any attempt at a procession would be illegal and see participants prosecuted.

Organisers are predicting several thousand people will attend today's Fans Against Criminalisation (FAC) protest in Glasgow's George Square – organised on the back of the incident which saw Celtic's self-styled "ultras", the Green Brigade, clash with police last month.

The group was accused by senior police officers of attempting to organise an unauthorised march against the Offensive Behaviour at Football legislation when the disorder erupted on March 16, sparking 13 arrests and a week of fall-out and criticism of police tactics.

Glasgow City Council declined to grant permission for FAC to parade through the city, as the organisers had not complied with the required 28 days notice to hold a street procession.

Permission for the group to hold a rally in George Square from 12 noon until 1:30pm was granted. Although permission is not required for static protests, the fact George Square is officially a city park means a protest requires approval from the land owners, the council.

Chief Superintendent Andy Bates, commander of Police Scotland's Greater Glasgow Division, said: "Clearly, as permission for a public procession has not been granted those attending the rally need to understand that any procession along the road from George Square would be illegal and anyone involved could find themselves subject to prosecution.

"It is important for their own safety and the safety of other road users that they don't block the roads as they leave the square.

"To reduce the risk of congestion we have identified three separate routes to the stadium leaving from George Street, Cochrane Street and South Frederick Street on to Glassford Street."

A Glasgow City Council source said: "The FAC submitted notification for a procession, but not within the statutory period. We declined, as there were no exceptional circumstances about the choice of date."

A spokesman for FAC said it had received permission for a static demonstration in George Square. It added this will "go ahead as planned. We hope many people will come and show their opposition to police aggression and to the Offensive Behaviour at Football Threatening Communication Act".