We are coming up for a general election here.
The main three in Britain are Labour (centre-left party, currently in power, will have ~40% of the vote I think); Conservatives (aka Tory party, Right wing party, will take 30 - 35% of the vote most likely) and the Liberal Democrats (far left party that masquerades as centreist, hated by all other parties, will take about 20% of the vote).
smaller parties include the British Nationalist Party (nazi's), The Monster Raving Loony Party (they are for something, but nobody is entirely sure what), UKIP (aka United Kingdom Independance Party - a Tory offsplit that is basing it's campaign on removing Britain from Europe and fiercer asylum policy), The Greens, a few others.
Regional Specific parties include SNP (Scottish National Party - left wing I believe, all for taking scotland out of the UK), Sein Fein (terrorist front for the IRA in North Ireland) and probably a welsh party of some kind.
Hope that helps.