Ed Miliband's policy of no new coal without carbon capture and storage (CCS) is certainly ambitious - but it represents a leap of faith almost as impressive as the Chancellor's Budget predictions.

The Energy Secretary wants as many as four CCS demonstration projects built, based on the expectation that the technology will be commercially viable by 2020. This, however, is by no means assured.

Small projects have succeeded in Germany and Canada but there is uncertainty over whether the technology can work on the scale required to make a difference in tackling climate change.These plants will be enormous: think of a structure the size of two Wembley stadiums. They represent a mammoth technical and engineering challenge. CCS is hugely energy-intensive - and there is the issue of how huge quantities of carbon will be piped out to subsea rock formations that formerly held natural gas.

The scientific principles underpinning each stage of this process are well understood, but putting all of this into practice could take far longer than 2020 and could be very expensive.

The Government could not say if the coal plants would operate “untreated” if the demonstration projects didn't work. It was also unclear just how the Environment Agency would make its decision over when CCS was viable.

Then there is the issue of cost and whether Mr Miliband is exposing consumers to huge overruns. Still, he deserves plaudits for trying. This is bold policymaking of the kind that may be necessary to deal with a global challenge.

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