Yea theres already a lot of backlash even with shit like the UK openly banning pro Pali protests...a rule which was defied massively
The UK actually didn't ban pro-Palestine protests. France and Germany did. The UK's pro-Palestine protests were fully legal, to the point that the Labour party had to tell its MPs not to go to the protest with the party's banner, because "individuals will not have the ability to control who they are photographed alongside and this risks threatening the Labour Party's ability to campaign against any form of racism and discrimination"
What happened in the UK is Suella Braverman, the Home Secretary,
gave the police advice on public order offences:
“It is not just explicit pro-Hamas symbols and chants that are cause for concern. I would encourage police to consider whether chants such as: ‘From the river to the sea, Palestine will be free’ should be understood as an expression of a violent desire to see Israel erased from the world, and whether its use in certain contexts may amount to a racially aggravated section 5 public order offence.
“I would encourage police to give similar consideration to the presence of symbols such as swastikas at anti-Israel demonstrations. Context is crucial. Behaviours that are legitimate in some circumstances, for example the waving of a Palestinian flag, may not be legitimate such as when intended to glorify acts of terrorism.
“Nor is it acceptable to drive through Jewish neighbourhoods, or single out Jewish members of the public, to aggressively chant or wave pro-Palestinian symbols at. Where harassment is identified, I would encourage the police to take swift and appropriate enforcement action.
“I encourage all chief officers to ensure that any protests which could exacerbate community tensions by way of offensive placards, chants, or behaviours that could be construed as incitement or harassment, have a strong police presence to ensure perpetrators are appropriately dealt with, and that communities feel protected,” she wrote. Home Office sources confirmed her words had been approved by government lawyers.
Decisions on arrests are an operational matter for the police, Braverman wrote. “However, I would urge you to ensure your forces use all available powers to prevent disorder and distress to our communities, and that your officers will act if there are any incidents that stray into criminality,” she said.
The human rights barrister Shami Chakrabarti said “[that] the letter had been so readily press-released suggests that the intervention is at best virtue signalling and at worst seeking to compromise operational independence”, adding: “Police chiefs know their powers and duties. Anxious and vulnerable minority communities are not made safer by the politicisation of policing in difficult and dangerous times.”
The way Public Order Offences work is basically if you do something with the intent of causing alarm, distress or intimidation and people feel alarmed, distressed or intimidated, then it's a crime - but you could do the same thing in a different context and it isn't. So for example, walking along waving a Palestinian flag isn't illegal, but standing outside a synagogue waving a Palestinian flag could be a Public Order Offence. Same deal with swearing - it's obviously not illegal, but if you stand in the street shouting swearwords at everyone passing by then that is a Public Order Offence (and then there's different levels e.g. arguing with a group of trans women you've met in a pub that they're men is not a public order offence, yelling it outside a transgender club is more of an offence, and following a trans woman to yell "you're a man" in a way that's especially threatening is even more of a public order offence).
Generally speaking police will usually just try and move someone along to diffuse the situation (British police are quite different from American police in that regard, although I think "I don't want the paperwork" is universal). Hence how you end up with a scene like this:
For context that this is Vahid Beheshti, who lives in a tent outside the Foreign Office and has been on "hunger strike" since February - he's an British Iranian activist who wants the UK Government to classify the Iranian armed forces as a terrorist organisation. He specifically put up an Israeli flag to antagonise the protesters who he kept calling Islamists, IRGC terrorists, "Khamenei's Basijis" etc. etc. so they nicked the flag off his tent and then he chased them down and grabbed it back and it devolved from there.
The police factor provocation into their response so it's not unusual for a protest of this size that the outcome was basically separating him from the mob and telling the mob to move on (and wouldn't have arrested anyone if they did, not sure if this was one of the arrests).
Additional context on this one - the "No Surrender" flag identifies this lot as members of one of the many descendants of the EDL (English Defence League), who are specifically anti-Muslim. No Surrender actually comes from an old anti-IRA chant which English football hooligans chant to piss off Irish teams and Celtic fans. The bloke flicking his v's on their flag is this photo-

- which was a skinhead getting arrested at a National Front demo in the 1981 (the National Front were openly white supremacist and wanted to deport every non-white person from the UK and also any white people who'd gone out with or were going out with someone who wasn't white).
Basically, they came to have a fight, and they got one.
Don't let this be taken to suggest I think "randomly beating up people in the street because you don't agree with them" is a good thing, because I don't, but one thing I will say for the British police (who are usually useless) is they're good at recognising agent provacteurs will turn up to these things to rile people up into a fight.