How accurate are they?
Labour: working-class benefits scrounger, illegal immigrant, asylum seeker, or all three. Plus the "champagne socialists" (rich progressives), who are seen as eating tofu and hummus, as well as being knee-jerk Anti-Tory and having an obsessive desire to be identified with the working-class. Will inevitably morph once in office to become ultra-authoritarian. Spend all the money they have and indeed, the money they don't have. If this spending results in increased efficiency (however small), it is obviously a massive success. If it doesn't work, throw more money at it and the problem will sort itself out.
Conservatives: Upper-class public-school toffs who want to take more money from the poor to give to the rich, and have duped the workers. They are either mocked as ultra-traditionalist "Shire Tories" who live in the countryside and are obsessed with the nobility and Victorian values or otherwise seen as slimy young middle-class libertarians who want to abolish the NHS while everyone's backs are turned.
Liberal Democrat: Cloudcuckoolander who believes his party will ever get in power, or alternatively Labour-lite or, more recently, Tory-Lite. Now actually in power. Once a party which was seen as 'trendy' to support, 'cos the others were too mainstream or somethink. these days, also stereotyped as somewhat hypocritical for forming a coalition with a party they had previously talked about as if it was their archnemesis.
Green : The Bog-Standard Green Stereotype. Bunch of bonkers hippy throwbacks, probably want to extend voting rights to fish, want the NHS to give more priority to crystal healing than heart transplants, are inherently suspicious of anything that could conceivably benefit humanity.
British National Party: Racist. Although they've recently been forced to allow non-white members to join and many actually have. These non-white members are also racist. For example, a Sikh man who hated Muslims was delighted to find like-minded comrades in the BNP. Their main enemies are of course the awful Muslamic ray guns.
UKIP: A bunch of xenophobic Little Englanders. Obsessed with the World War 2 and compare the Third Reich with the EU constantly. Either seen making tired national stereotypes about the French or fervently campaigning against political correctness. Reads the Daily Express. Believes the EU had banned bendy bananas and cars with more than three wheels. Has obsessed fantasies about launching their own resistance movement against the evil Europeans.
SNP: Bunch of whiny Scots who watched Braveheart and decided that it should be brought into the 21st century. Basically Labour but more mawkishly nationalistic. Leeches money off English people while claiming they don't need it.
Plaid Cymru: Have a stupid name, obsessed with the necromancy of a long-forgotten and incomprehensible language, physically incapable of doing anything constructive in power. Basically think of all the stereotypes of a Welshman and imagine a whole horde of them. Charming, eh?
Respect: A hodge-podge alliance of aging, unwashed liberals ready to scream "Military-Industrial Complex" if they so much as see a soldier walking to the news-agents, and bearded Muslim Fundamentalists hell-bent on imposing Shariah law in London.
Sinn Fein: Terrorists who have accidently become politicians. Never show up for work, not that they would get let in if they did.
"DUP" : Really, really, really conservative. Thinks gay people are abominations or something like that.
"Independents" : Too ugly/egotistical to join a real party. http://tvtropes.org/pmwiki/pmwiki.php/Main/PoliticalStereotype