Assistant Chief Constable Andy Holt told reporters before the team's opening match against France that fans dressing in England kit made their job harder.
One of the reasons is that the worldwide popularity of the English Premier League has created a generation of fans who support top English clubs as well as their own local teams and many people from neighbouring Russia are expected in Ukraine to cheer on England over the next two weeks.
"We have seen quite a lot of Russians with England shirts on - that's great if they are supporting England of course," Holt said.
"But if there is some disorder and it appears they are wearing an England shirt, I want my officers to go in there and establish what we're dealing with so we've got it first hand, so we know whether it's an English fan and we have a problem or whether actually it's somebody from another nation who supports another team who just happens to have an England shirt on.
Holt said that there was usually very little problem with England fans nowadays.
"We have worked very hard to make sure that England fans are policed appropriately and if England fans do engage in disorder that we know about it and are able to deal with that." he said.
"But what I don't want is to have England fans mislabelled, and misidentified because it's some other nationality wearing England shirts so you can imagine we will be very careful to ensure that if there is any problems, we identify the provenance of who we are dealing with."
Around 5,000 England fans are expected to attend England's three group stage matches against France and Ukraine in Donetsk and Sweden in Kiev and they are being marshalled by uniformed British officers, who, Holt says, have built up a very good working relationship with them.
Twelve police officers are in Donetsk for Monday's match with four others working as spotters in Poland and generally the relationship between fans and police is vastly different from the days when England supporters were responsible for widespread hooliganism across Europe.
"Perhaps 20 years ago the fans who caused problems were very wary of the police, because they knew we were gathering evidence on them, going back to the UK, and getting football banning orders on them," Holt said.
"Now we get a warm and cordial welcome from our fans abroad, they see us as a re-assuring presence. Fans must be judged on their behaviour today and not the old reputation of the past."
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