Q+A - Where might parties agree after election?

LONDON (Reuters) - The nation is set for its first hung parliament for 30 years in which no party has overall control, according to opinion polls showing a tight race between the three main parties in the run-up to a May 6 election.

The normally third-ranked Liberal Democrats are preparing to play kingmaker after polling day between Labour and the Conservatives.

Q: WHAT IS THE PRICE FOR LIB DEM SUPPORT?

A: Above all, voting reform to a more proportional system that would better align votes cast and parliamentary seats won. On equal shares of the national vote under the current winner-takes-all constituency-based system, Labour would win three times as many seats in the 650-member parliament as the Lib Dems, and the Conservatives twice as many.

Q: WHAT ARE LABOUR AND THE CONSERVATIVES OFFERING?

A: Neither party is promising the kind of proportional voting the Lib Dems want, aware that it could destroy their chance in future of ruling alone with an outright majority.

The Conservatives are the most opposed to a proportional system. Labour have promised a referendum on a modest change to the voting system, with some senior Labour politicians in favour of going further.

Q: DOES THAT RULE OUT LIB DEM SUPPORT FOR EITHER PARTY?

A: It may prevent a formal coalition, but may not preclude a looser deal to support a minority government's financial budget while not being bound on other legislation.

Q: WHAT ELSE DO THE LIB DEMS WANT?

A: The party has set out three other priorities for any post-election talks:

-- Extra money to boost school education for the poorest young children. The Conservatives have similar plans. Labour says it is already doing this, but could probably agree to the Lib Dem proposal.

-- A reform of personal taxation to benefit lower-paid workers by closing "loopholes" that benefit the rich. This is more radical than anything offered by Labour or the Conservatives.

-- A reform of the economy with less dependence on the financial sector, splitting up banks that are "too big to fail." Both Labour and Conservatives want to take further action to avoid another banking crisis, but disagree on the detail.

Q: WHAT HAPPENS IF NO AGREEMENT IS REACHED?

A: Labour or the Conservatives would have to rule as a minority administration, daring their opponents to vote down their legislation and risk a fresh election.

Q: WHAT IS THE COMMON GROUND BETWEEN ALL PARTIES?

A: All parties agree on continuing Britain's military role in Afghanistan, levying taxes on banks, and promoting a greener economy.

Q: WHERE DO THE LIB DEMS AGREE WITH LABOUR?

A: The two parties agree on delaying spending cuts and tax rises to tackle a huge budget deficit until next year, to avoid sending the economy back into recession, unlike the Conservatives, who would start a fiscal squeeze this year.

They also share a positive approach to the European Union, unlike the eurosceptic Conservatives, and agree on constitutional changes that would introduce fixed-term parliaments and reduce the voting age to 16 from 18.

Q: WHERE DO THE LIB DEMS AGREE WITH THE CONSERVATIVES?

A: On civil liberties they are much closer to the Conservatives. Both parties oppose Labour plans to introduce national identity cards and the retention of innocent people's DNA in a police database. The two parties also both want to reduce the number of members of parliament, to cut tax breaks for better-off families, and to drop plans for a new runway at London's Heathrow airport on environmental grounds.

Q: WHERE ARE THE LIB DEMS ISOLATED?

A: Both Labour and the Conservatives want to replace Britain's ageing Trident submarine nuclear weapons system. The Lib Dems say Britain cannot afford the 100 billion pound price tag for a "like-for-like" replacement and want a defence review to look for a cheaper alternative.

The Lib Dems also oppose a Labour-Conservative consensus on building new nuclear reactors, favouring renewable energy and conservation measures instead.