Here is the link to make an online complaint at the press council.
Imagine complaining to them about a view expressed by Oprah Winfrey. If your complaint is about something GT said on a TV show (including the nightly news), then that is how they will regard your complaint.
But if about something he said in a newspaper, then they will look more closely. In this case, the first thing they will consider is whether the article is "news" or opinion.
I believe GT contributes opinion (aka "commentary") only, so this licences him to say whatever he likes and speculate as much as he likes.
I believe that any complaint to the Press Council would be a complete waste of time.
Why aren't you targeting the producers of the TV shows he appears on? GT is just the messenger. It is the producers that like his message and insist on bringing it to us.