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A top British actress who starred in Harry Potter is leading a campaign for justice for Steven Avery and nephew Brendan Dassey by protesting outside the US embassy in London next month.

Miriam Margolyes OBE, who starred as Professor Sprout in the movies, says she is outraged by the "injustice" in the case made popular in documentary Making a Murderer.

And she was so furious after watching the Netflix show, she even sent personal letters to Steven and Brendan.

The 74-year-old says she has been "sickened" watching the show insisting officials at Manitowoc County in Wisconsin are "wicked".

She added that Mr Avery and his family have been a victim of the system and were picked on because of their "class."

Ms Margolyes says she feels for the family and in particular Delores Avery - the mother and grandmother of both Steven and Brendan.

(Image: PA)

Speaking exclusively to Mirror Online she said: "Nothing about this case stacks up, absolutely nothing, it is absolutely sickening to watch what has gone on here, in fact I would go as far as to say it is utterly wicked.

"I am not a lawyer in anyway and I have watched the show like everyone else but I can truthfully say I think the whole thing is absolutely sinister.

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"The Avery family have been a victim of the class system from start to finish, it is clear they have been treated like they were trash and by a group of people who were, in my opinion, colluding.

(Image: Youtube/Netflix US & Canada)

"I cannot truthfully say from the bottom of my heart what went on, all I can say is that something is not right here."

Miriam who has recently returned from India from filming her reality TV show The Real Marigold Hotel says she has been in touch with the Avery family and that she's hoping that she can add weight to their campaign.

She added: "I have written to both Steven and Brendan and of course the Avery family and I offered to go out there and lend my support.

"If I can go to Wisconsin I absolutely would, I think these people have to understand that there are others in the world that feel for them on a very human level.

"There are many terrible, terrible things happening in the world right now with war but this television show has sparked attention because it's unjust.

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"I cannot pretend to understand what is going on in America anymore, I think this show is a zeitgeist and has captured the mood of a nation.

"The fact that they took that young 16-year-old boy in for questioning, without his parents, without a lawyer and extracted that confession out of him beggar's belief.

"It was an outrageous manner of interrogation and should never have been admissable.

"Then you have to look at the evidence. There simply wasn't any that actually stacks up."

Miriam will join protesters in London on April 2 as they take their campaign to British streets.

Hundreds of activists plan to visit the city for the rally in Parliament Square and then at the US Embassy to protest at what Miriam calls "a gross miscarriage of justice."