Which specific departments. You both are talking in such broad terms about different events and trying to generalize to all police, all Nazi's and all anti fascists.
What would the police you work with do if they local Nazi's used the same techniques of violating the assembly route to mix it up with the counter protesters, while carrying shields and clubs? And the counter protesters did have a permit here, and as far as I can tell it was the Nazi's who violated their permit first.
From my experience, it doesn't matter who is creating the public nuisance, the police are impartial. The thing is, in the UK,groups such as the EDL generally
want to be allowed to march, so they do what they have/need to do in order to still be able to continue marching. They
can cause trouble, but they're usually pretty amicable, they turn up, march, and leave. Their marches are annoying, because they take up police time, and require additional groups, such as hired security groups, etc. This is made easier for all due to them properly organizing the march, making it easier to plan manned guards along the prearranged route and set up cordons where necessary.
Problems arise when counter groups just turn up randomly, for obvious reasons. The already limited police and security are stretched to their limits, and the potential for trouble is obviously high. You've got to consider the fact that this is usually in an already busy town center, with average members of the public going about their business. It disrupts everything, and instead of having an organized march, you end up with warfare.
If the EDL did the same thing, and randomly turned up to create havoc, then the police and the security groups would in the exact same position as the one I mentioned. It's nothing to do with AntiFa or the EDL, it's to do with the obvious problem of having a routine march become a problematic battle between two groups of individuals who are creating a public nuisance, potentially damaging public property, causing issues for local businesses and all other manner of problems that the police and the security services could honestly do without.
People tend to forget that the police and security are there to do a job, a job they get paid the same wage as other police and security get for doing less stressful work.
There's no conspiracy, no favouritism, there's just a bunch of limited people doing far more work than is necessary. We'd much prefer peaceful protests all-round, but that almost never happens.
Why? a lot of police are politically aligned with the white supremacists views of this protest. There are all those regular scandals about the police violating the constitutional rights of blacks at a higher rate than whites, being more violent toward blacks and of course using racial epithets in official communications.
Your attempt to equate the situation in Britain with the situation in the US is pretty laughable. I bet if avowed racists shot and killed 5 people in Britain durring a strike in 1978 who belonged to the communist workers party they might even have been prosecuted. Now that is how you stage a real counter protest. None of this namby pamby antifasc BS. The KKK knows how to get things done.
https://en.wikipedia.org/wiki/Greensboro_massacre
Not all police are aligned with white supremacists at all, though. People are people, no matter their position, so you'll always have room for such things, but it's not the norm, not here, anyway.
I'm not equating anything, I was giving an example of why AntiFa members can and do get arrested, because I've seen it up close and personal on many many occasions.
You can't claim that the AntiFa are out for peaceful protests when they're wearing disguises and carrying bricks and bottles, whether in the UK or in the US. It's common sense, really.