Which policies are you thinking of?
Green policy on Drugs I believe to be quite sensible, similar to the dutch model, but more support through NHS for hard drug addicts (e.g. Heroine addicts)
Their Energy policy is good in principle but would either not be different to what is being done already, OR will need a HUGE sum of money to get it done in a relatively quick time (30 years or so). They want pretty much 100% renewable energy, which can't be done, not until technology in renewables significantly makes them more efficient.
Drugs policy is an interesting area. If you approach it from an economic standpoint, I think it might be more cost-effective to have a policy based on treatment and intervention aimed at managing the problem, coupled with looking for alternatives for those using the stuff - which in turn gets into trying to understand why they are using. Is it a personal issue around addictive personality? A social thing about peer groups and lifestyle? Is it related to limited economic prospects?
In most cases, money spent on trying to understand and treat the issue would be more effective, and would produce a better quality of life for the rest of us, than an approach based on trying to catch them after their four hundredth burglary and bang them up for a few months, releasing them to go back to the same old thing.
But we seem to have a policy based a little more on the idea of punishment, and treatment as something which should play a minor role rather than the main plank of policy.
I reckon this more liberal policy wouldn't cost more, probably less, and would be more effective in curbing both drug use and the unpleasant impacts on the rest of us.
Energy - tough one. We've known since at least the 70's that our current energy policy can only lead to recurrent energy crises, economic destabilisation, and environmental catastrophe. We also know that there are alternative technologies which can help deal with a large part of the problem. We know that they require big investment to make them work, that the private sector won't lead the way, but that if there are enough tax penalties for bad energy use and rewards for good energy use, then people very quickly change their behaviour, firms (for example) start making windows and boilers with greater thermal efficiency, the costs fall because production is on a larger scale, and it all becomes a bit more affordable.
If you see a change in energy policy as something which must be wholly state-funded, then it's unaffordable without massive tax increases. If the government chooses to create costs and benefits to encourage and discourage certain behaviours, then it starts to look more affordable, as in Germany for example (they haven't got their energy policy sorted and foolproof, but they seem a bit further down the road than us).
But really, the question is not whether we need to invest much, much more in renewables. It's how, and how quickly, we can do so. Timid nods in the direction of a few wind farms while appeasing the oil companies really won't work.
In the same way, recognising that radical changes in energy policy are needed, while voting for people who won't make this change, won't work either.