Labour: they are the most left-wing party out of the three you mentioned. Labour believe in equality and fairness, and want to reduce the gap between rich and poor. They want to stay in the EU and limit immigration (but to a much smaller extent than parties such as the Conservatives or UKIP.) Essentially, they see immigrants as contributing to the economy. In terms of the economy, they will cut spending, but not as hard and deep as the Conservatives have, who Labour believe have stagnated economic growth by cutting public spending too fast. Essentially, they'll cut less, and invest more to stimulate economic growth. This is similar to what Obama did in the United States and what Germany were doing before 2011. The Labour Party is the party which created the NHS (free, universal healthcare) and advocate large social benefits to be given to the vulnerable. They decreased absolute poverty by 50% when they were last in power and relative poverty by 33%. As for foreign policy, they seem to have shifted back to a more traditional left-wing anti-war perspective, as they voted against the illegal war in Syria which the Conservatives were planning. Socially, they overwhelmingly supported gay marriage, and are the party who introduced civil partnerships and who decriminalised homosexuality decades ago. They're more left-wing than Obama and the Democrats in the U.S., and the current leader of Labour, Ed Miliband, has the support of the trade unions and had the support of Tony Benn, an influential far Left figure in the Labour movement. Miliiband's father, Ralph Miliband, was a Marxist academic.
Conservatives: they are a centre-right party, who believe in what they call "equal opportunities", which basically means that everybody has the opportunity to have something or to get somewhere, but only a certain rich elite will be given the job or the position in the end. Their frontbenchers and leaders want to stay in the EU, but there is a large portion of the party which does not want to stay in the EU. They want to limit immigration to a fairly large extent, and recently suppressed a report which demonstrated that, in actual fact, immigrants do not "steal" British jobs. As for the economy, they like the private sector more than the public sector, and enjoy privatising everything - they are trying to privatise the East Coast mainline, despite the fact that when it has been nationalised, it's performed better than all the other railways which are privatised. They are a party for the rich, essentially. They recently gave a tax cut to millionaires, and you will regularly see their Chancellor, George Osborne, going off to Brussels to try to maintain bankers' ridiculous bonuses. Under their Dear Leader, Mrs. Thatcher, inequality and poverty soared, and we're seeing that again today with them in charge. As for social benefits, they see everyone on benefits as scroungers who are lazy. As for foreign policy, the Conservative Party are the only party who defend the Iraq War to this day, and wanted to take us into an illegal war in Syria last August. Socially, almost half (45%) of their members of Parliament voted against gay marriage. They're certainly less right-wing than the Republicans, though.
Liberal Democrats: they're quite mixed at the moment: they're pretty much a centrist party, with some left-wing elements. They're in power currently, in a Coalition with the Conservatives. They've advocated many of the Conservatives' harshest policies, including the 'bedroom tax', which means that some benefits are deducted from people who live in council houses with spare rooms, including 350,000 disabled people, who need the rooms to store vital equipment. Nick Clegg, the leader of the Liberal Democrats, has been defending many of the Conservatives' policies. Having said that, their President, Tim Farron, is more left-wing, and has spoken out against the bedroom tax.
As for the May election next year, Labour are currently on course for a majority, according to the polls. However, I suspect it'll be a Hung Parliament again, meaning that another Coalition government will have to be formed. The Conservatives almost certainly won't get a majority: if they couldn't get one in 2010, the likelihood that they'll get one after they've ruined our country is extremely slim.