Sir Iain Duncan Smith has been left "astonished" by a decision to clear a man accused of assaulting him by "slamming" a traffic cone on his head because of "weak" evidence.
Elliot Bovill was charged along with two other protesters who shouted "Tory scum" at the MP as they followed him through a city centre.
Sir Iain told Manchester Magistrates' Court he feared for his wife and her friend when he had the cone "slammed" on to his head as they were followed by protesters hurling abuse during the Conservative Party Conference last year.
On Tuesday, the chief magistrate, Senior District Judge Paul Goldspring, said the evidence that identified Mr Bovill, 32, of no fixed address, as the person caught on CCTV putting the orange and white cone on the 68-year-old MP's head was "weak" and "tenuous", and dismissed the common assault charge against him saying there was no case to answer.
The 68-year-old told the Daily Mail he was "astonished", and that the decision sent out a message that politicians were "fair game".
He said: "Seemingly you can now walk down the street screaming abuse at me, and your right to protest trumps my right not to be intimidated.
"No matter how threatening the behaviour of protesters is, no action will be taken against them."
Mr Goldspring later acquitted co-defendants Radical Haslam, 29, of Douglas Street, Salford, and Ruth Wood, 51, of Oak Tree Avenue, Cambridge, of using threatening, abusive or insulting words or behaviour with intent to cause harassment, alarm or distress.
The chief magistrate said the case against Mr Haslam and Ms Wood centred on the use of the phrase "Tory scum" by the pair as they followed him and the two women along Portland Street in Manchester.
Mr Goldspring said using that phrase in the context of them targeting Sir Iain as they followed him was "both insulting and pejorative, and I don't accept that that wasn't their intention".
But he accepted that this behaviour was "reasonable" in the context of Articles 10 and 11 of the Human Rights Act - the rights to freedom of expression and freedom of assembly and association.
He said: "The courts do not criminalise free speech. The Crown has not shown me it is proportionate to criminalise those words."
But he stressed that his decision that the use of the words "Tory scum" was not criminal was only relevant to "this court, in this case, on this evidence" and could not be applied to other contexts.
Earlier, Mr Goldspring told the court that Mr Bovill had been identified by a detective on the basis of poor-quality CCTV footage which was shown to the court on Monday.
The chief magistrate said: "It seems to me there are a number of difficulties with the identification that had been made.
"The fact is that what (the officer) was working with was vague and flawed in the first instance.
"In my view, the identification evidence is weak, it's tenuous, and it is completely unsupported by any other evidence."
On Monday, Sir Iain said he was already feeling threatened by the protesters who followed him on October 4 2021 as he left the conference at the Midland Hotel and walked with his wife Betsy and her friend Primrose Yorke to the Mercure Hotel, where he was due to speak.
He said he turned around after the cone was "smacked down" on his head and told the group "you are pathetic".
He said he was particularly concerned for the safety of his wife and Mrs Yorke.
His wife told the court the group that followed them from the hotel "used the c-word, the f-word, they called us scum, Tory scum".
Lady Duncan Smith said "it was getting quite nasty" as they were confronted with a "barrage of rudery".
Wood, who manages a project for a homelessness charity, denied calling the group "c----", saying it was "problematic terminology" she would not use.
She told the judge: "Radical was making some quite good points, I thought. I wasn't really chanting very much. I was pretty much just drumming along.
"There was nothing particularly threatening about what we were doing, in my mind.
"Not once did he turn round or try to tell us to stop. It just didn't seem to me as if they were concerned at all."
Asked about the cone, Wood said: "It seemed to me at the time like a practical joke."
Haslam, who said he was a writer, poet, general artist and Manchester Metropolitan University student, added that he saw it as an "opportunity to have my voice heard".
He said: "We saw a politician and saw an opportunity to express our political views.
"We live in a democracy where protest is legal. I was hoping for some sort of exchange."
The defendant agreed that he shouted a series of comments at the MP, saying "shame on you", in relation to a range of policies relating to child poverty, climate change and homelessness.
He said he was making a speech which, he accepted, ended with the phrase "Tory scum".
Asked about the cone incident, Haslam said: "He (Sir Iain) didn't come across as alarmed or distressed. He came across as angry that it had happened."