A little-known group of conspiracy theorists has shot to national prominence in America after supportive T-shirts and banners were spotted in the crowd at a Donald Trump rally this week. 

QAnon, which is based on the idea that a secret government official is leaking information to bring down the anti-Trump ‘deep state’, has been largely found in obscure internet chat rooms since its emergence last year. 

But on Tuesday evening it triggered headlines across the country as supportive messages were spotted being displayed by some attendees at Mr Trump’s campaign speech in Tampa, Florida. 

Television cameras captured people holding posters aloft saying “we are Q” or carrying references to the group’s…