But there aren't - poorer people would want a much more socialist regime than even the lib dems or the greens could provide. The extremely rich and selfish people would want to go back to back to the "laissez-faire" ways of Victorian Britain. Some centre-right people may not feel that the Tories are credible enough and so spoil their paper. Others with extreme nationalistic views without a BNP candidate in their area would want to spoil their paper.
In my opinion though - anyone who is a socialist should support which ever party has the best prospect of heading towards left away from the centre if enough people who would benefit from them weren't apathetic, be it the greens or the lib dems.
174 parties have their name registered in England only, 367 in the UK
http://en.wikipedia.org/wiki/List_of_political_parties_in_the_United_Kingdom
Sure, not all of them stand in each area, but there is usually a lot of choice.
I think its a gross generalisation that poor people vote socialist and rich people vote right wing. Yes, there is some correlation, but not everyone votes for themselves. I certainly don't, choosing which party represents the overall *vision* I'd like to see at the current time, and a lot depends on what you believe: For example, do you believe the state is better is organising things or the individual, or a mixture of both. Are you a traditionalist or a reformer, or even a mixture? Do you believe in top down management, or people organising themselves and social/personal responsibility?
There is such a thing as liberal left (like the libdems to an extent) or authoritarian left (like the Labour party to an extent).
There are very right wing Tories like John Redwood, and left wing ones like Philip Blond. There are very left wing people in the Labour party, like John Prescott and right wing ones like Tony Blair.
Of course some people never ask themselves these questions, vote for themselves, some even do life style votes where they vote on perceptions of image.
There's also nothing wrong with the centre (all the main parties are centralist), it doesn't mean you can't make up your mind. To some people the state is better at running some things (like health, education, some transport), but they would be appalled by the idea of state run restaurants, hair dressers and toy and humbug manufacturers.
There are many ways of organising business as well.
The best thing is to read and find as much as possible on everything you can, and then read and find out about what the political parties stand for and go from there based on how you want to vote.