It is a truth that is uncomfortable as standing beside one of England’s “idiots” – to quote the FA’s own video warning of this – but the trouble we all saw in Porto has been simmering for some time.

It was not just a sudden outbreak. The reality is this is the natural step up from the type of behaviour we saw in Seville. This is the next step when your standard behaviour is occupying a space in a foreign city as if it was a political statement, singing politically loaded chants that dementedly reference past violence, and then acting as if you are the offended party when anyone dares to say they disapprove of this.

A low-intensity obnoxiousness gave way to some high-profile trouble, of the type that very few other countries or clubs seem to get involved in. This, in short, was coming.

For their part, the police had warned of it. The FA knew of it. This is why they released that very video, with the message “don’t be that idiot”. Too many were, again. It is a minority, yes, but a depressingly sizeable minority.

A statement from Deputy Chief Constable Mark Roberts said it is believed the trouble started when England fans began throwing bottles at home supporters from Portugal, who had been watching their 3-1 win over Switzerland in the fan zone.

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That had only followed incidents the previous night outside a bar when bottles were thrown and minor damage caused. “It is completely unacceptable,” as Roberts said.

It also stands out all the more when, just days ago, as many as 100,000 fans of Liverpool and Tottenham Hotspur went to Madrid and were generally lauded for good-spirited behaviour.

There may have been isolated issues, but that’s the point, as it is with pretty much all of the Premier League club supporters who go abroad. You just don’t see this.

There is a huge difference between isolated incidents and this kind of mass occupation that is almost shepherded by this unifying atmosphere of abrasiveness, and given an outlet in the anachronistic nonsense of songs like “f**k the Pope”… and finally violence.

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This is a culture that has become so troublingly distinctive to the English national team and it would, frankly, be ludicrous not to link it to the specific type of nationalism that has become so prevalent in the country. You can hear mentions of Brexit in so many chants. You could even see some fans refusing to go in the EU queue for passport control in the airport.

This isn’t to say that all of these fans responsible for trouble are a result of this. The FA have for a long time now been conscious of a “stag party” element to the travelling fans, where young professionals in their mid-20s go away with England and feel they can just let go. Some, evidently, feel they can let go of deeper-seated political feelings.

How else to explain the constant references to the Second World War or the conflict in Northern Ireland? It is admittedly very difficult for the governing bodies to get ahold of, especially when a fan group culture now feels this ingrained.

The FA can refuse to give certain fans tickets, and those with convictions can be barred from travel, but it’s impossible to stop everyone else descending on a foreign city – particularly one so easy to get to.