Yes - he was detained by the Heathrow Police - who are routinely armed. The tweets in question were one stating
"If a trans-identified male is in a female only space, he is committing a violent abusive act. Make a scene, call the cops and if all else fails punch him in the balls"
I can see why this tweet MIGHT be looked at by police. It is on any sensible reading an attempt at humour ( not in my view humerous). No serious interpretation of this could regard it as an incitement to violence and in any event it says "if all else fails..." it is a huge hurdle to e passed before the suggestion of punching is made
Second tweet was a picture of protestors with the legend "a photo you can smell"
I struggle to see what criminal offence can possible be made out by this tweet. It may be offensive to some people, but that does not make it a crime. You do not have the legal right not to be offended ( as Ricky Gervais amongst others has said so eloquently in the past)
Third tweet referenced the photo and said "I hate them. Misogynists and homophobes" followed by an undetermined expletive.
This is no more than an expression of his opinion. It is not inciting anyone to do anything. If he hates homophobes and misogynists, then he is entitled to that opinion
Whether or not you agree with Linehan, this does seem to be palpably absurd and a waste of taxpayers money.
I agree, but I would go much further and say it is a rather worrying- attempt to criminalise free speech.
I would think that there is a case for saying this was a potentially unlawful act by the police. That is without bringing into question whether the use of the powers of arrest were lawful and whether he should have been (if these tweets were to be investigated), invited to attend an interview as a voluntary offender as per the leading case of Mark Richardson v The Chief Constable Of West Midlands Police [2011]EWHC 773 QB . The fact that someone is suspect of a crime or is wanted to be questioned about a crime is not of itself sufficient alone to justify an arrest.