Law professor Geoff Pearson himself infiltrated supporters' clubs in the early 2000s. Today, the groups are the subject of his research at the University of Manchester.

According to him, the explanation for the decrease in violence lies partly in a better dialogue between supporters and the police – but also in tougher measures regarding access bans.

"You are banned not only from the stadiums but also from the surrounding area," he explains.

Italy, in turn, has gone even further in terms of access bans. Listen to SVT's Italy correspondent in the clip:

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How stricter rules have given safer stands in Italy – hear SVT's Italy correspondent in the clip. Photo: SVT