Arsenal will investigate how vast numbers of Cologne supporters gained access to the home sections of the Emirates Stadium for Thursday’s Europa League match, sparking crowd trouble.

The Group H opener, which Arsenal won 3-1, was delayed by an hour as ticketless Cologne fans sought to gain entry to the ground.

Visiting fans were issued with 3,000 tickets but around 20,000 fans of the German club are believed to have made the journey to London.

There were clearly thousands of away supporters sitting among Arsenal fans, causing a security risk.

Five arrests were made and Arsenal issued a statement on Friday insisting the safety of supporters was the main concern at the time.

“Following last night’s Uefa Europa League match with Cologne we would like to stress that fan safety was always our paramount concern and informed all decisions made,” it said.

“We have launched a full review into the circumstances surrounding the game and will ensure any lessons that can be learned are used in the future.”

A Uefa probe is also likely after pictures emerged of a minority of Cologne supporters causing problems for stewards inside the stadium.
When the game eventually kicked off, Arsenal fell behind early on to a brilliant long-range strike from Jhon Cordoba before bouncing back in the second half, substitute Sead Kolasinac equalizing before goals from Alexis Sanchez and Hector Bellerin saw the Gunners to victory.

Afterwards, Arsenal manager Arsene Wenger said he was getting ready for the game to be postponed but was uncertain if the delayed kick-off was to blame for the Gunners’ poor start.

“It’s difficult to say,” he said. “It was similar for Cologne but we had some problems to get off, to start, yes. I don’t know, was it mental?

“We waited patiently in our dressing room but what was difficult for me have I had all kind of plans to think about at some stage.”

Wenger added: “I had to think if we play tomorrow at what time do we want to play, do we play next week but they had the Bundesliga again midweek and we had a League Cup game midweek as well.

“But in the end at some stage, I thought they would not play the game because I can’t see the police taking any risk,” he explained.

“We live in a society of 100 per cent security and I thought they would never take a gamble to play this game when I saw the images around the stadium.

“But I must say our supporters dealt well with the situation as well and there was no aggravation.