The security breach at Wembley Stadium which saw fans without tickets get into the Euro 2020 final took police by surprise, Scotland Yard has said.
Deputy Assistant Commissioner Laurence Taylor said officers had planned for London to be busy with supporters, but did not expect stadium security to be compromised.
Footage posted on social media showed people forcing their way through barriers and a line of security staff before rushing up the escalators ahead of Sunday’s final between England and Italy.
Mr Taylor told the PA news agency: “We spent a lot of time encouraging and asking people not to turn up if they hadn’t got a ticket prior to the event, and clearly a lot of people chose to ignore us.”
He said nobody was expecting “large numbers of people” to try to get into the stadium.
“As soon as it became clear that was happening, stewards reacted very quickly and police were deployed to the stadium to prevent the situation from becoming worse,” he added.
He said a “considerable number” of fans got into the ground, although he was not able to estimate how many.
“As part of our post-event investigation, we will be looking into all criminality and we will be looking to bring offenders of any crime to justice – that may include football banning orders as well as criminal justice prosecutions,” he said.
It came as the fallout from England’s crushing final defeat continued.
The Metropolitan Police made 86 arrests on Sunday for “a variety of offences” including drunkenness and assault.
Nineteen police officers were injured, including one who lost a tooth in the disorder, while another suffered a broken hand.
Mr Taylor said: “No assault on any officer is acceptable. Police officers are there doing the job to keep people safe, and it is totally unacceptable that anybody thinks it’s OK to assault the police.”
He said investigations into disorder were ongoing, and added: “I hope the vast majority of people will be as appalled as I was by the behaviour of a few.
“Hopefully that doesn’t reflect everybody in this country.”
Police forces across the country dealt with 875 football-related incidents, with 246 arrests made so far, according to the National Police Chiefs’ Council.
Chief Constable Mark Roberts, football policing lead, said: “Although the result wasn’t what we hoped for last night, it’s absolutely no excuse for the appalling behaviour we have seen across the country.”
Elsewhere, England players Marcus Rashford, Jadon Sancho and Bukayo Saka – who all missed penalties during the penalty shoot-out – were all targeted by online trolls.
The Duke of Cambridge, who is president of the Football Association and watched the final at Wembley, was among those to condemn the racist abuse.
William wrote on Twitter: “I am sickened by the racist abuse aimed at England players after last night’s match.
“It is totally unacceptable that players have to endure this abhorrent behaviour.
“It must stop now and all those involved should be held accountable.”
England manager Gareth Southgate described the abuse as “unforgivable”.
“It’s just not what we stand for,” he said during a press conference on Monday.
Prime Minister Boris Johnson said: “This England team deserve to be lauded as heroes, not racially abused on social media. Those responsible for this appalling abuse should be ashamed of themselves.”
Meanwhile, Downing Street ended hopes that England’s best result in a major tournament since 1966 would be marked by a bank holiday.
The Prime Minister’s official spokesman said: “We’ll be talking to the FA to identify a suitable way for the Prime Minister to thank the players and coaching staff for their efforts. But a bank holiday is not something that is being considered.”
Elsewhere, Wiltshire Police said they made seven football-related arrests, with three further arrests by Bedfordshire Police.