After excavating your mega-basement in Holland Park, it's cheaper and easier to leave the JCB entombed down there with the pool, personal cinema and staff quarters.

A new solution emerged: simply bury the digger in its own hole. Given the exceptional profits of London property development, why bother with the expense and hassle of retrieving a used digger -- worth only £5,000 or £6,000 -- from the back of a house that would soon be sold for several million? The time and money expended on rescuing a digger were better spent moving on to the next big deal. [...]

How many of these once perfectly functioning and possibly still serviceable diggers are petrified underneath central London, like those Romans preserved cowering in the corners of houses in Pompeii? Estimates vary. One property developer I asked reckoned at least 1,000; another put the figure at more like 500. In some of London's newest luxury conversions, "sub-basements" are being tucked beneath the existing basement conversions. But developers are stumbling on a new kind of obstacle as they burrow deeper still: abandoned diggers from the last round of improvements.

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