It's hard to imagine anything more at odds with the hi-tech, microwave, designer-kitchen age than the Aga cooker. It's formidably heavy. It's far from cheap to buy and install. And yet its popularity has grown and grown since it came to England from Sweden in 1929. More than just a commercial success story, it has come to symbolise the quintessence of upper-and middle-class rural life. In Chiswick and the Isle of Dogs it suggests the warm heart of the English country home. How did it happen?