Labour: Democratic Socialist/Social Democratic. Socially moderate. Tied to the Unions (hence the name). Large Christian Socialist wing. Supported by blue collar/low income voters, Non-Conformists, Progressive Yuppie types (not in local council elections though) and certain ethnic minorities (esp. Sikhs).
Closest party in the UK to the Democrats in the US.
Conservatives: Conservative. Split between "Wets" (moderates) and Right wingers. Supported by high income voters, High Church Anglicans and better off farmers.
Closest party in the UK to the GOP.
Liberal Democrats: Mixed. The "Big L Liberal" wing is very strong in rural areas and tends to be socially moderate and pro-gun/fox hunting etc. The "Liberal Suburbanite" wing is socially liberal and right wing on economics.
There is also a small Social Democrat wing (a hangover from the SDP) although it's large at local level.
Other Parties;
UKIP: [Far] Right-wing, anti EU, Isolationist etc. Came third in the European Elections. Mostly a protest party.
SNP: Scottish Seperatist/Nationalist. Ranges from far-right to far-left depending on what part of Scotland they are in.
Plaid Cymru: Welsh Seperatist/Nationalist. Tends to be left of centre (although Welsh politics is *very* left wing), supported by Welsh Speakers and certain middle class voters. Used as a protest vote sometimes.
Greens: Guess.
BNP: Neo-Nazi thugs
Respect-The Unity Coalition/SWP/SA/Etc Ad Nausem: various far-left groups. Little public support.
Thanks AL, BTW who is John Prescott?