The seed bank estimates that it will need about £100 million over the next decade to achieve its mission to rescue one-quarter of the world's plant species. It's a large bill at a time when governments around the world are facing serious financial problems -- especially that of the United Kingdom, which is a significant funder for the project -- and philanthropic sources are also drying up.
But Smith points out that the figure actually equates to just £2,000 per species.
Fearful of 'faddism'
The picture varies around the world, with both China and the United States maintaining funding flows for plant species collection, while in Africa, some projects have come to a dead stop.
In part, this is due to political changes of mind, and in part, it is because the seed bank is the main or sole funder of some of the projects, and its own future funding is uncertain.
"The financial side is the immediate problem, and the political standoff at and after Copenhagen doesn't help," said Smith, speaking of the U.N. climate negotiations in the Danish capital last year. "The politics has always been less than perfect. My fear is that it will get substantially worse. There has always been a problem of faddism in development policy."
The Millennium Seed Bank is cooperating closely with the food crop seed bank project on the frozen Svalbard archipelago in northern Norway, which holds samples of 526,000 unique crop varieties sent for safekeeping from existing collections around the world.
The drive behind the cooperation is the Crop Wild Relatives program, which is based on the premise that as food crops have been derived from once-wild species, they are likely to still have close links with them, although some key genetic traits such as hardiness and drought resistance might well have been bred out of the domesticated varieties.
So the Wakehurst Place scientists and seed collectors will index these wild relatives when they find them and therefore act as another crucial resource for the food crop scientists in Svalbard and elsewhere.
"Crops like the staples wheat and maize of today are a long way from what they used to be. Those lost genetic traits might prove vital in the coming changed climate," said Smith. "Also bear in mind that many of the food crops we take for granted now at home actually originated on other continents. For example, wheat originated in Egypt, and potatoes came from the Andes."
And some of the troubles to come are already visible.
In the United States, pine bark beetles have already devastated vast areas of woodland, and in the United Kingdom, the oak processionary moth has hit both trees and people, as the very fine body hairs of the caterpillars cause skin and respiratory problems.
The spread of both has been attributed to climate changes.
Facing the daunting array of difficulties, Smith is undeterred in what some may see as his mission impossible.
Wakehurst Place is aiming to cut its carbon footprint and its energy bill with a wind turbine, solar photovoltaic panels and a wood-gas-powered combined heat and power unit, all of which should help also raise its public profile as it continues the battle to save as many of the world's plants as it possibly can.
"My message to the politicians is this: The technological problems are surmountable. We have the networks and the momentum. The problems are urgent and getting more so. We need to scale up, not cut back. Give us the resources to get on with it, and we can do the job," he said.