At jsut £2, supermarket chickens have never been so cheap

Yet this is how the superstore retailer is marketing its £2 medium-sized British chicken, claiming that the cheap bird's powerful allure makes it one of the few products for which customers will 'cross town' to pop in the shopping trolley.

Indeed, weighing 1.55kg and sporting a Union Jack label to assure buyers of its provenance, the Asda chicken is flying off the shelves - with shoppers capitalising on the lowest poultry prices for decades and buying them three a time.

It's a symbol of a remarkable shift in eating patterns and proof of the way chicken has become the latest weapon (many would say victim) of the supermarket price war.

The big question is: how on earth is it possible to sell a chicken at such an extraordinarily low price? Today, a plump, tempting bird is as much a staple of most supermarket trolleys as bread, but this was not always so. Prior to World War II, there was no real market for broiler chickens - birds farmed for meat alone.

Chickens consumed in the 1930s and 1940s were typically laying hens which were slaughtered and roasted only when they had reached the end of their egg-producing lives.

But, in 1953, when post-war rationing on animals was lifted, farmers realised there was money to be made from marketing chickens purely for eating - and the broiler chicken industry started to grow, independent of the egg business.

Advances in veterinary medicine - in particular the arrival of antibiotics for animals - made it possible, and profitable, to keep large numbers of birds together in a small space. Before antibiotics were added to animal feed, birds had to be kept in far larger spaces to avoid the spread of disease.

The chickens we eat today (with the exception of free-range and organic birds) are typically reared indoors in large sheds, crammed 17 or 18 to a square metre.