How will the PM cut energy bills?

It was an announcement made under pressure, an announcement that, so far, is little more than a headline. An announcement that left the prime minister's coalition partners complaining about a panicky U-turn.

However, this was not a policy simply made up on the morning after Sir John Major's call for a windfall tax on the energy companies.

Behind the scenes David Cameron and Nick Clegg have discussed the need to get household bills down. Cabinet Secretary Sir Jeremy Heywood had been tasked with examining the taxes and the regulations that have helped drive them up.

Today the prime minister was focussing on what he said was the green part of the average household dual fuel bill - £112 - or just under a tenth of the total.

But the Lib Dems insist that only £50 of that really subsidises things like wind and solar power. The other £62, they say, is help for householders - subsidies for greener boilers and insulation, things that will long term help keep bills down.

The four men who run this coalition - the so-called "quad" - will now try to hammer out a deal on which parts of those, if any, can be cut.

They are also hoping the energy regulator and competition authorities will find a way in the next year to create a more competitive and transparent market.

So, today we got a new prime ministerial promise to cut energy bills. Just one thing we're waiting for - the news of how and by how much.