A chicken squats in a shed the size of a football pitch somewhere in the outback of Brazil. And it’s not alone.

One of tens of thousands, each bird is allowed the floor space equivalent to a sheet of A4 paper and will live for just 40 days before it hits its genetically-engineered slaughter weight. That’s if it doesn’t perish along the way.

Five per cent or so will be unable to cope with the conditions and die even before then.

Those that survive will be plucked and butchered in an industrial process the like of which this planet has never before seen.

Every year billions of chickens will live and die in this way. Of course, South America is a long way away. But your local McDonald’s is not. And that is where a significant proportion of this intensively reared meat will eventually end up.

Of all the chicken churned out by the fast-food chain – the equivalent of 30 million birds a year – 60 per cent is imported frozen from Brazil. A further nine per cent comes from Thailand and 30 per cent from Holland

A quick bit of arithmetic reveals just how much of the chicken sold in the fast-food giant’s British restaurants is reared in this country: that’s right, just one per cent.

It’s a figure that’s never before been published, and it will surprise and disturb many. After all, in recent years McDonald’s has effectively relaunched itself as a chain that cares about the provenance of its food and its relationship with the nation’s farmers.

There have been television adverts featuring bucolic rural scenes, paper tray mats that introduce the customer to the chain’s suppliers and a website that boasts of lovingly nurtured, homegrown spuds.

The beef they use is sourced entirely from British and Irish farms, the eggs free-range, the milk organic and the coffee beans Rainforest Alliance-certified.

And, clearly, it is something that chimes with the public. During the past four years, McDonald’s UK had added £465million to its sales, while in 2009 there was a double-digit increase in like-for-like sales as customer visits rose year on year. In terms of growth, Britain is leading the way across McDonald’s international empire.

Impressive stuff, and it’s not just the public who are reacting well. This month, the celebrity chef Jamie Oliver publicly gave his backing to the chain.

‘The quality of the beef, they only sell free-range eggs, they only sell organic milk, their ethics and recycling is being improved and improved,’ he said in an interview. ‘And I can’t even believe I’m telling you that McDonald’s UK has come a long way, but actually, it probably puts quite a lot of gastro-pubs to shame, the amount of work they’re doing in the back end.

‘Also, they’ve just had their best commercial year in four years, so they’re proving that being commercial and caring can work. Actually, it’s the future.’

But what – and it is a very big ‘what’ – about the chicken, the dish which one suspects many customers seeking a healthier option would generally go for? What aspect of these birds’ life cycle, of the impact their production has on the planet, could possibly be described as ‘caring’?

More to the point, is it something about which Jamie Oliver or the millions of customers who eat in McDonald’s every week are even aware?