MY parish here in the City of London will be a battle zone when the G20 summit of leading nations opens next week. Gangs protesting about the wars in Afghanistan and Iraq will bring fights to the streets of London.

The rabble so anxious to save the environment will vandalise their own capital city.

People who pretend to care for all humanity will beat the living daylights out of anyone in their way. The mob complaining about the misappropriation and waste of money will, by their violence, force a police operation costing more than £10m.

The police have given us warning that 1,000 protestors will converge on the Bank of England – that’s 200 yards from my church’s front door. I have already seen a poster: “BURN A BANKER”.

The police statement goes on to say: “A hardcore of protestors is intent on storming buildings and promoting violence. Everything is up for grabs. The intention is to get in and clog up the City.”

The protestors themselves are threatening “a summer of rage”. There is delicious irony in the fact that the protests are largely about “global capitalism”, yet the organisers are setting it all up using mobile phones and the internet – the hallmark tools of international finance and entrepreneurism.

I was engulfed by this sort of aggression and vandalism when I hadn’t been long here in my parish of St Michael’s, Cornhill. Eight years ago, I was standing at the altar saying the Friday lunchtime Mass. There was a background rumble, muffled at first, but growing steadily louder. Then the anarchists’ trademark whistles and the thuggish chanting as they lurched their way down Cornhill towards Bank station. They were still trundling past when the Mass had ended.

I was struck by the hatred in the painted faces of the mob.

Still in my vestments, I walked down the steps to the roadside where I was accosted by a couple of thugs. “What the f*** are you doing for anti-capitalism, mate?” I was asked.

“Only this,” I said, as I raised my right hand and started saying the Exorcism Service in Latin. The police were unprepared and outnumbered on that occasion and the City was left like a bomb site with more than £2m damage.

There was considerable violence against the police and one mounted officer was lucky to escape with his life, as the thugs tried to bring him down. The authorities promise they will be better prepared this time.

I don’t blame the anarchists. They are, by definition, the enemies of law and order and all government. But I do blame the “useful idiots”

– as Stalin called the unthinking crowd which tags along with them. It’s appropriate that some of the demonstrations will take place on April Fools’ Day.

There are things mightily wrong with the way the Government and many financiers have been handling our money. And we have a bad record when it comes to looking after the environment – though it is depressing to see the bishops swallowing whole the great global warming fraud.

But vandalism, violence against the person and a colossal hatred for our City, nation and institutions is no answer to the huge problems which beset us. The nihilistic louts who will descend on London are great haters.

They hate us all. I suspect they even hate themselves.

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