Actually, this approach has nothing to do with easing the UK's cash flow problems. Money that is handed over to this development fund will never come back to the UK treasury. It is gone, just as surely as if it had been given as an outright grant.
The funds -- supplied by the UK and other G8 nations -- would be administered by the World Bank. The World Bank has been remarkably effective in aiding the development and economies of lesser-developed nations. It is a very effective way of preventing economic imperialism, by nations making grants directly.
These World Bank loans would be made on "concessionary" terms -- meaning long payback periods, and very low interest. The effect of the loans would be considerable economic benefit for the borrower nations, over time, and teh benefits would eventually provide enough income to service and repay the loans.
It is no different than when the World Bank advances a nation funds to build a large hydroelectric dam. Such a dam not only provides needed electricity, at a low cost, but greatly aids agriculture and prevents devastating, costly floods. Over time, it creates enormous economic benefit.
We can argue all day long about whether global warming is in fact a real phenomenon, and if so whether or to what extent it is man-made, and who or which nations may have caused it. In my view, it is entirely unreasonable to assert that because a nation is prosperous, it should bear the costs of correcting climate problems in nations which are not prosperous -- and try to justify that view by claiming that the prosperous nations caused the climate to change.
Earth has experienced many climatic changes in the past, some very sudden and extreme, some going from cold to hot and others going from hot to cold. We may be entering such a change at present; but the experience of the past couple of decades is too brief to be persuasive (despite Al Gore's claims). But even allowing that the climate is changing and the oceans will rise, pointing the finger of blame at a few nations, or a few asserted causes, is simply irrational.
That said, I am all in favor of the World Bank, and its mission to aid in development of smaller and less mature nations. Funding of the World Bank should of course come from the prosperouos nations, because poor nations do not have the resources to fund the Bank. The World Bank, to I think the greatest extent possible, de-politicizes these development programs, and removes any influence of individual large nations over the recipients of those loans.
Mr. Brown may or may not deserve the scorn some people lay on him. But it is quite clear that the UK contributions to this World Bank fund have no benefit for him, nor for his government. They are a wise use of British funds, as they are for the funds of other contributing nations. In this case, Mr. Brown is no more than an agent of doing good for the lesser-developed nations of the world.