Freedom of speech is actually written into the human rights act.
First, "freedom of speech" is a legal principal that exists to ensure freedom from government persecution. "Without interference by public authority" - that's a direct quote. It solely and exclusively refers to people having the right to not be persecuted or oppressed (eg imprisoned or arrested) by the government or other authorities due to what they've said.
"Freedom of speech" has nothing whatsoever to do with forcing people to give you a platform for your views. There is NO right or law that compels a commercial venue to give someone a platform. We can argue that a commercial venue made a bad decision to cancel the show but they are 100% within their legal rights.
Freedom of speech laws would only apply as JS had been arrested or imprisoned due to what he said. He hasn't, so the Human Rights act is completely irrelevant in this specific case.
Second, the Human Rights Act contains numerous exceptions where it's very explicitly spelled out "you do not have freedom of speech under these circumstances." The Human Rights Act explicitly states that governments can overrule freedom of speech, and that people do NOT have the right to freedom of speech, if that speech would endanger national security, harm someone else's reputation or endanger someone else's rights, breach confidentiality, incite crime, or incite hatred.
This is a direct quote from the Human Rights Act:
"2. The exercise of [freedom of speech] may be subject to such restrictions or penalties as are prescribed by law and are necessary in a democratic society, in the interests of national security, territorial disorder or crime, for the protection of health or morals, for the protection of the reputation or rights of others, for preventing the disclosure of information received in confidence, or for maintaining the authority and impartiality of the judiciary."
The Human Rights Act explicitly says that freedom of speech is not absolute, and that freedom of speech does not apply to certain things. Using racial slurs could be considered to be a breach of hate crime legislation, and hate crimes by definition are excluded from freedom of speech in the human rights act.