Liverpool have called for an investigation into the "unacceptable issues" faced by fans which led to their Champions League final against Real Madrid being delayed.
Uefa delayed kick-off by more than 30 minutes, citing "security reasons".
The match at the Stade de France in Paris did not start until 20:36 BST, with Real beating Liverpool 1-0.
Police outside the ground fired tear gas as a small number of supporters tried to climb over security barriers.
UK sports minister Nigel Huddleston tweeted: "We are very concerned about the upsetting scenes around the Stade de France last night and shall be working with the appropriate authorities to find out what happened and why."
Liverpool defender Andy Robertson said the organisation of the match was a "shambles".
Merseyside Police said its officers who were deployed in Paris and attended the match "reported the vast majority of fans behaved in an exemplary manner, arriving at turnstiles early and queuing as directed".
"Our officers returning today will conduct a formal debrief to ensure that we can fully support any subsequent investigation following last night's game," said assistant Chief Constable Chris Green.
Merseyside Police's matchday officers tweeted that it was "the worst European match I've ever worked or experienced".
They added: "I thought the behaviour of the fans at the turnstiles was exemplary in shocking circumstances. You were not late 100%."
Liverpool Mayor Joanne Anderson criticised the "appalling management and brutal treatment of fans" and said she would be writing to Foreign Secretary Liz Truss "requesting answers from Uefa and for [France's] President Emmanuel Macron to investigate".
Liverpool fans' group Spirit of Shankly said the situation was "totally shambolic and extremely dangerous."
Pictures had emerged in the build-up of huge crowds of fans queuing to get in.
Many claimed they had been at the stadium hours before kick-off but were stopped from getting into the ground.
"We are hugely disappointed at the stadium entry issues and breakdown of the security perimeter that Liverpool fans faced this evening at Stade de France," the Anfield club said in a statement.
"This is the greatest match in European football and supporters should not have to experience the scenes we have witnessed tonight.
"We have officially requested a formal investigation into the causes of these unacceptable issues."
On Sunday, Liverpool chief executive Billy Hogan said the club wanted supporters to come forward with their experiences to feed into any investigations.
"We want to provide those facts to the relevant authorities," he said.
"In the coming days, we will be setting up a mechanism for supporters to reach out to us directly to provide their experiences and accounts of what happened."
European football's governing body Uefa said it was "sympathetic to those affected by these events and will further review these matters urgently together with the French police and authorities, and with the French Football Federation".
"In the lead-up to the game, the turnstiles at the Liverpool end became blocked by thousands of fans who had purchased fake tickets which did not work in the turnstiles," it explained.
"This created a build-up of fans trying to get in. As a result, the kick-off was delayed by 35 minutes to allow as many fans as possible with genuine tickets to gain access.
"As numbers outside the stadium continued to build up after kick-off, the police dispersed them with tear gas and forced them away from the stadium."
French police had urged fans not to force entry with tweets 20 minutes before the game was scheduled to begin.
As kick-off approached, large areas of empty seats could still be seen inside the ground.
Outside, some fans were seen climbing perimeter fences or attempting to run past security. Riot police were also in attendance.
Liverpool players emerged to warm up again at 20:06, with messages on the big screens inside the stadium stating the delay was because of the late arrival of fans.
French police said fans with fake tickets had tried to force access to the stadium but "the rapid intervention of the police allowed the return to calm".
They added they were able to disperse fans "without difficulty".
They also said there were no major incidents at fan zones in the city, although 500 people were moved on from a bar near the Liverpool fanzone at Cours de Vincennes.
French sports minister Amelie Oudea-Castera tweeted: "The attempts at intrusion and fraud by thousands of English supporters complicated the work of the stadium staff and police but will not tarnish this victory."
While interior minister Gerald Darmanin also blamed British fans.
'A completely unreasonable situation' - the fans' view
BBC journalist Nick Parrott, who was outside the ground in a personal capacity, told BBC Radio 5 Live: "I have just been pepper sprayed for the first time in my life. I have been to the Champions League final before and I have never been pepper sprayed before.
"I was outside Gate Y which has been opening and closing repeatedly over the last hour and a half but nobody has been going through. The security staff on the other side advanced and sprayed pepper spray."
The opening ceremony started at just after 20:20 BST before the game finally got under way 16 minutes later.
Some 10 minutes after kick-off, Football Supporters Europe said "thousands are still trapped outside the stadium, remaining calm in the face of a completely unreasonable situation".
The body added: "Fans at the Champions League final bear no responsibility for tonight's fiasco."
BBC Sport's John Watson, at the ground, said he had "passed hundreds of Liverpool fans queuing at entry gates an hour before kick-off and not being permitted entry".
"I'm at a loss to understand the reasoning for the delay being the late arrival of fans," he added.
Defender Robertson says he had given a ticket to a friend but he was denied entry for the game.
"One of my mates got told it was a fake which I assure you it wasn't," he said.
"It was horrendous for our fans and all families that have been through it as well. It wasn't a nice experience, not a nice final to come to. The Champions League should be a celebration but it wasn't that."
Liverpool West Derby MP Ian Byrne tweeted to say he had "endured one of the worst experiences in my life", blaming Uefa for "horrendous security and organisation putting lives at risk".
"I pray no fans have been injured because of the disgraceful lack of organisation and expertise," he added.
Dominic King, from the Daily Mail, told BBC Radio 5 Live he had been speaking to supporters queueing to get into the stadium.
"It came from nowhere," he said. "There has been no violence or antagonism. They are just dismayed by how the authorities have treated them."
"We got told about 45 minutes before, that our end was filled while there were thousands outside," Liverpool fan Tyler, who spent £1,000 on his ticket, told BBC Radio 5 Live.
Fans also said they were assaulted and robbed by local gangs when leaving the stadium following the match.
Former Liverpool defender and now television pundit Jim Beglin was among them and tweeted: "Post-match last night was the scariest I've ever experienced.
"Organised gangs set about mugging departing fans. We ran a gauntlet of thuggery on our way to the Metro. Not a police officer in sight. Witnessed so many ambush attacks on unsuspecting attendees. Reprehensible."
The final was originally to be played in St Petersburg, but the city was stripped of the game following Russia's invasion of Ukraine.
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