BARRING disasters as yet unknown, the tackling of the national debt is the biggest challenge facing the next Prime Minister.

How will his government – red, blue, or yellow – manage to cut the country’s mind-boggling deficit without damaging the fragile economic recovery and pushing us back into a dreaded double-dip recession?

It is the hardest question facing the would-be prime ministers and yet it is a question none is keen to answer.

Indeed, the reticence of the three main parties over the fiscal repair job was underlined yesterday by the Institute of Fiscal Studies (IFS) as it predicted that the UK faces the deepest spending cuts since the late Seventies.

IFS director Robert Chote criticised all three parties for failing to spell out their budget plans more clearly to voters.

Tomorrow night’s third and final televised leaders’ debate, chaired by David Dimbleby and focusing on the economy, is an opportunity to pin down Gordon Brown, David Cameron and Nick Clegg on this vital issue, in front of millions of viewers.

The question about where the axe may fall was put to Mr Cameron by Jeremy Paxman last Friday, and the Tory leader stirred up a hornets’ nest by talking about the North-East and Northern Ireland.

Honesty is what the voters want from politicians, but the politicians know that a really honest answer on public sector spending cuts would scupper their chances.

It is a question none of the party leaders wants to answer in meaningful detail – but it is a question that must be pressed.

Over to you, Mr Dimbleby.