Scientists said they could ease a key doubt that clouds "clean coal" - the dream of harnessing a fuel that is as cheap and plentiful as it is environmentally dangerous.

China, India and other countries have ramped up burning of coal this decade to power their growth and brake their dependence on expensive imported oil.

By doing so, they have also cranked emissions of carbon dioxide (CO2), the heat-trapping byproduct of this dirty, low-energy fuel.

A powerful lobby has emerged, sustained by the coal industry itself, to argue that with financial help and innovation, "clean coal" lies just on the horizon.

This term refers to a basket of technologies, the biggest of which is carbon capture and storage, or CCS.

Under CCS, power stations would burn coal but siphon off the CO2 at source before pumping the unwanted gas into deep chambers underground, such as disused gas or oilfields.

The CO2 would be stored there indefinitely rather than be disgorged into the atmosphere to add to the greenhouse effect.

Ecologists and geologists have sounded a loud word of caution: What are the guarantees that these chambers are leak-proof? A breach would surrender the man-made CO2 to the air, amplifying global warming.

In a study published in the journal Nature, a British team give a qualified "yes" to that question. So far, attempts to investigate the leak issue have been limited to computer simulation and a few small-scale pilot studies in the North Sea and the US, which have only been going on for a few years.