HelmsleY - flash floods - global warming. That was the sequence of words that leapt out of the radio yesterday morning.

I've driven over that bridge in Helmsley scores of times on my way to Rievaulx Abbey, calling in first at The Black Swan where they do a substantial afternoon tea - and they have a ghost.

But have we gone barmy or what? I mean, you can't get a summer thunderstorm nowadays without the parroting of the apocalyptic mantra "global warming". All my life we've had summer cloudbursts and just now and again something spectacular. I recall a 12-hour thunderstorm over Leeds at the end of August 1960. Lads coming back from a night out at The Capital ballroom thought it was the end of the world and our sins were catching up with us. Was that caused by global warming too? In those days all the media talk was that, far from hotting up, the climate was about to deliver another Ice Age.

But "global warming" has become one of those uncontestable modern dogmas - like "institutional racism" and "we are all to blame". You might delude yourself that we live in a free society but, when it comes to global warming, you'd better be careful what you say. Scientists who dare to question whether global warming is actually happening, whether it's being caused by greenhouse gas emissions or not, are outcast by their own profession. I read over the weekend about the many researchers into climate change who cannot get their findings published in leading scientific journals because they refuse to accept the imposed orthodoxy that global warming is happening and it's all our fault.

This is totalitarianism in action, involving as it does the suppression of ideas and free speech. Funny thing, free speech in Britain today: say anything, filthy or blasphemous on the stage or TV and no-one bats an eyelid, but try to question one of the politically correct orthodoxies and you'll be punished. The sceptical environmentalist Bjorn Lomborg has even had death threats.

Look, this has nothing at all to do with whether global warming is happening or not. It has everything to do with whether one is allowed to suggest that it isn't. Surely, science of all human enterprises ought to be free to question ideas and beliefs? Nobody minds if scientists question the Bible's account of creation.

So why is there effectively a police state when it comes to the issue of global warming? First, because global warming has become an unassailable orthodoxy and there are vast government grants towards its investigation. Second, there is a widespread prejudice and hatred of capitalism, the globalised economy and especially America. (Just wait until the million politicised yobs and thugs turn out to destroy Edinburgh next month at the G8 summit).

For the record, there is considerable doubt as to whether global warming is happening at all. There is even more doubt that such warming as might be happening is caused by anything human beings are doing. Much likelier that it is a blip in a natural cycle. And even if global warming is being caused by emissions from factories and cars, most of this is generated not by Europe and the US but by China, India and the former Soviet Union. Am I allowed to say this, please?

* Peter Mullen is Rector of St Michael's, Cornhill, in the City of London, and Chaplain to the Stock Exchange.