There seems to be a fundamental misunderstanding about the term "free speech", that somehow anyone is allowed by law to say anything they like no matter how inflammatory so long as they believe it to be the truth. "I can say whatever I like, mate - we have free speech in this country, innit!" Er, no you can't, mate, because we don't!
UK citizens have what is termed a "negative right" to freedom of expression. However, this is not a blanket authorisation by any means, as there are many exceptions set down in law. Plus, the UK's laws on defamation, slander and libel are some of the toughest in the world.
Good explanation here:
https://en.wikipedia.org/wiki/Freedom_of_speech_by_country#United_Kingdom