Far-right marches led by the self-styled "Danny Tommo" should not be treated like normal protests, the communities secretary, Angela Rayner, has said, calling the marches "intimidation" that should not be permitted.

Rayner said the behaviour of some masked marchers – who have blocked roads and transport hubs – was not an acceptable form of protest.

Daniel Thomas, the instigator of the marches over the past month, was arrested and charged last week after allegedly using a blade to slash an inflatable dinghy in the Channel while a rescue worker was onboard.

Rayner said the marches were frightening local people. "When you see hundreds of predominantly men in black wearing black face masks shouting, going down the street, that is intimidating," she said. "Whether you agree with the message or not, it's intimidating."

She added: "It is not a protest. I've been on many protests myself when I was in my union days. We have music, we have banners, but we don't wear balaclavas and shout divisive rhetoric down the street.

"There's a line, and I think organising to disrupt and cordon off areas to stop people going through public highways, this is all behaviour that is intimidatory and is not acceptable."

Thomas has recently brought dozens of nationalist protest groups together under the umbrella name of Patriot Platform. Masked and hooded anti-migrant activists from the movement have convened in English coastal towns and ports, in one case blocking traffic in and out of the port of Dover.

Rayner said she was deeply concerned by the way social media was amplifying extreme voices – especially those targeting the RNLI.

On the day that a 10-year-old child and two women died ⁠attempting ​to cross the Channel, Rayner said there needed to be more humanity about how migrants were described and treated when they attempted to cross in small boats.

"How can we get to the point where we dehumanise like this," she asked. "Yes, we can have an argument about the criminals putting people on these boats, the legitimacy of someone's claim. But when you've got a human being at risk of death, do we let them drown?

"That is ultimately what it comes down to. Yes, we politicians have a discussion about policies, about people we give asylum to, about how we stop boats. But [to] attack volunteers that save people from drowning?

"These are volunteers. If there's a risk to life at sea, an RNLI volunteer without any political persuasion at all or any ideology will go out and will save lives at sea.

"To whip up hatred as if they are making a judgment on the value of these lives that they're saving or not, and to put their faces up, identify them, to whip up online hatred towards volunteers whose sole job is to give up their time to save lives at sea. It's not acceptable."