Police Scotland have condemned ‘the shameful behaviour of a number of supporters’ after Celtic and Rangers fans clashed on the pitch

Flares were thrown as supporters from both sides spilled onto the pitch after Celtic's 4-2 win on penalties.

As if the ugliness of the 120 minutes wasn't enough there was disgrace as Rangers and Celtic fans invaded the pitch at Ibrox, writes Tom English.

Police Scotland have condemned ‘the shameful behaviour of a number of supporters’ after Celtic and Rangers fans clashed on the pitch

After ugly scenes at Sunday's Old Firm derby, what do we know about the fan clashes and what could happen next?