If the last few years have taught us nothing (and there is copious evidence to suggest that they haven't) it is that a bank that is incapable of lending money is as much use as windscreen wipers on a submarine.
And yet despite this obvious reality, concerns are continuing to mount that the coalition's much-trumpeted Green Investment Bank is in danger of becoming a singularly futile institution.
As the group of 50 businesses, NGOs and MPs who wrote to the government today demanding clarification on the plans for the GIB accurately point out, everyone agrees with the green bank in principle. Private investors are simply too risk averse to provide the financing that cutting edge low carbon projects require at the pace and scale that is needed to meet the UK's carbon targets. As such a dedicated Green Investment Bank willing to take those risks and overcome those investment barriers is essential to the future of the UK's low carbon plans.
But such a bank can only work if it has access to cash - lots of it.
The Treasury is right to suggest that the bank could ultimately become self sustaining, raising funding through green ISAs and green funds. But during the first few years of its existence it will need some taxpayers' money if it is to make the kind of big ticket green investments that can be used to attract those private sector investors.
The group of businesses and NGOs today argued that the bank needs access to between £5bn and £7bn if it is to be successful, which in the current economic climate appears to be a classic case of asking for the world in the hope that you get something.
More realistic are Labour's plans to provide the bank with around £2bn, including around £1bn raised through asset sales such as the offloading of the channel rail link. But if reports are to be believed, the Treasury has already ruled out raising money for the bank through asset sales and seems to be investigating a far more modest level of investment based on savings realized through the merging of green quangos.
The sad truth is that supposedly flagship Green Investment Bank will be fatally holed below the waterline if it launches with a capital base of around £1bn that confines it to investing a couple of million quid in small scale low carbon projects.
The October spending review is fast shaping up as the ultimate test of the coalition's green credentials.
Green business leaders accept that some cuts have to be made, they accept that many green quangos should be axed, and that DECC will inevitably become a less significant force. But they will find it hard to accept cuts that water down election manifesto commitments and serve to make it harder for them to invest in the kind of low carbon projects that David Cameron insists he wants to see.
The future of the Green Investment Bank, the feed-in tariff programme and the Renewable Heat Incentive are fast shaping up as the true test of the coalition's green credentials. Fail to deliver on these issues and the coalition's green commitments will begin to look as bankrupt as a bank with empty vaults.
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