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

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

Celtic knocked Rangers out of the Scottish cup after winning a penalty shootout 4-2 following a goalless 120 minutes, before fans from both clubs invaded the pitch

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

Watch the moment fans clashed on the pitch after Celtic knocked Rangers out of the Scottish Gas Scottish Cup on penalties following a goalless draw. Dozens of Celtic supporters…

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