Why is it "colluding"? The people who operate these venues and the communities that they operate him may have simply discovered what he was.
They all discovered who Franklin Graham was at approximately the precise same time it seems.
If these venues are interested in protecting the ears and minds of their town folk then they should find out who these dangerous people are before agreeing to letting these evil monsters speak.
I don't know what the law is in the UK, but in the U.S. only the government is on the hook for a denial of free speech. It appears that your graham can speak anywhere that he can a room.
I doubt Graham will be able to
obtain a venue that accommodates more than a handful of people in the UK.
It's a nation of snowflakes now.
By your reasoning, the cult people are colluding against LGBTs.
No more than LGBTs "collude" against cult people, whoever that is. It's mutual dislike.
This is different than the Graham situation.
This collusion of Graham is signified by orchestrated and coordinated denial of service. Kind of like "we don't serve your kind" messages to certain types of people when they come to town.