So The Register is where the UK (Ex) Tech VC's hang out now!
... and here's another wading now!
Having done a bunch of "Cleantech" investments it seemed to me that nearly everything I saw that could make a really big impact was beyond the scope of any but the most long term and substantial VC fund.
The kind of stuff that makes a difference on emissions tends to be competing with an established technology that's had the benefit of many cycles of optimisation. So if my new cement production, metal winning, or energy storage technology has a chance it must reach the point where it is working at levels of optimization that also take several iterations to approach.
Stuff that's going to make a big difference often involves big equipment, that means that those iterations tend to often be much slower than for more traditional venture investments:if the technology involves plant and equipment or significant scale-up to become economic, then each cycle of improvement can be years. In a 10 year standard VC structure you can get 6 years sometimes (assuming you don't invest on day 1 and need some time to realise at the other end). That's a very tight constraint.
Back around 2002/3 lots of large US VC's moved towards cleantech generally- it was interesting to observe that they often moved their focus to software optimisations around the edges of existing processes for exactly these reasons.