I came across this interesting website that looks at how parties have shifted over the years - this first chart shows the shifts while the second chart places where the political parties are today - including the Green party.
A first glance confirms the shift in Labour over the years to the right - and indeed the Lib Dems. The Tories meanwhile have also moved a little - the differences between them are very small. Read more about it all here:
The website also has an interesting personal test that allows you to place yourself on the chart and see how close you are to a particular political party - it strangely put me very close to the Green party! It also looks at other elections like the US Presidential elections.
Lastly it is worth also mentioning the independent Vote for Policies, Not Personalities website (www.voteforpolicies.org.uk) that looks at policies - some 167,000 people have taken part and Greens are still ahead. Well worth a look. See also my post yesterday about every vote not being equal.