More than 400 police were on duty in and around St Andrew's - at least four times the normal presence at a game.

Seven supporters have so far been arrested and now officers are concentrating on identifying the troublemakers behind the ugly scenes inside the stadium after the final whistle.

Police will be aided in their task by the two clubs involved after both Birmingham and Aston Villa confirmed today they would work with them and the relevant authorities to help identify the culprits.

More than a thousand Blues supporters invaded the pitch within seconds of their side's 2-1 win - the first over Villa for five-and-a-half years - and confronted the 3,800 Villa fans situated in the Gil Merrick Stand at the other end of the stadium.

A flare appeared to be thrown into the section housing the Villa supporters, although it was then tossed backwards and forwards between the rival factions.

Seats were also ripped out and used as missiles along with other objects.

Supt Steve Graham, of West Midlands Police, said: "The passion we saw for 80-85 minutes was exactly what we are proud of within the English game.

"It is just a shame it spilled over into the criminal behaviour we saw on the pitch at the end.

"There have been seven arrests but that was over the course of the whole operation.

"When the pitch invasion occured, we were more concerned about asserting some control within the stadium and making sure the crowd dispersed safely and securely."

Supt Graham added: "We've started a post-match inquiry whereby we will seek to identify people who committed criminal offences.

"Sadly we've had some experience of this in the past although it is still an unusual event.

"But we will put steps in place now to idenify those offenders, prosecute them and, if they are convicted, they will be banned for a long time."

Supt Graham admitted: "I wouldn't say we were expecting trouble but we knew it was a strong possibility.

"It has happened in the past, we have got intelligence, and that's why we had the level of officers on duty that we did have."

Birmingham released a statement today saying that "no effort would be spared" as they endeavour to help identify the culprits.

Blues officials met this morning and after agreeing to conduct their own investigation also pledged to enforce "stringent action" on those fans found guilty of any disorder.

A further meeting with officials at Aston Villa, the local authority, safety advisory committee and the emergency services has also been set down for next week.

The Blues' statement read: "No effort will be spared in Birmingham City football club's efforts to identify individuals who marred the Carling Cup quarter-final victory over Aston Villa.

"Blues are extremely disappointed that the scenes after the full-time whistle took the gloss off the club's progression to the semi-finals of the competition.

"As well as identifying and punishing any trouble-causers the club is also determined to maintain the family-friendly atmosphere inside the stadium that only a couple of years ago saw the club win football's Family Excellence Award.

"Anyone who threatens to derail Birmingham City's ethos of welcoming families to the stadium is not welcome at St Andrew's and actions like those of certain individuals on Wednesday night will not be tolerated."

The Football Association have also indicated they will carry out a full investigation and called for any identified culprits to be banned, although no definite action will be taken today.

An FA spokesperson said: "We wholly condemn the actions of any individuals who have been involved in the scenes of disorder at St Andrew's.

"The FA abhors acts of violent behaviour and we urge the clubs and authorities to identify any individuals involved in disorder, and impose the stiffest available sanctions, including banning orders.

"The FA will fully investigate the matter in conjunction with the appropriate authorities.

"The whole of English football has worked hard to eradicate scenes of disorder from our game.

"Home Office figures this week show a significant drop in arrests at the many thousands of football matches held every week, the majority of which still pass trouble-free."

Villa also pledged full co-operation with the FA and relevant authorities.

A club statement read: "Following the scenes in the aftermath of the Carling Cup quarter-final at St Andrew's, the club will co-operate fully with the FA in its investigation in conjunction with the appropriate authorities."

Birmingham clinched a two legged semi-final tie with West Ham - and their former owners David Sullivan and David Gold - thanks to a late goal from Serbia international Nikola Zigic.