The leaders of Ukip, the Greens, the SNP, Plaid Cymru and Labour will go head-to-head at the event in central London but the Conservatives and Liberal Democrats will not be involved.
Speaking ahead of tonights event, Jonathan Arnott, the Ukip MEP for the North East England, told Premier's News Hour that Ukip will cut the aid budget from 0.7% of GDP to 0.2%.
"At the moment we're giving aid to 19 of the 20 most corrupt countries in the world. We're giving aid to countires in the G20, countires with nuclear programmes, with space programmes.
"What we believe this aid should be about is giving for countries to make sure they've got, for example clean water supplies, to deal with things like the Ebola crisis, with tsunamis, with natural disasters.
"That's what people expect foreign aid to be for and that's what we should be giving - and I believe that those amounts of money would still be giving quite generously to those things."
In March the UK passed legislation officially committing to maintaining the level of foreign aid at 0.7% GDP. It was the first G7 country to meet the UN's 45-year-old aid spending target.
The Conservatives want to protect the foreign aid budget and the SNP wish to maintain 0.7% commitment to foreign aid. Plaid Cymru is in agreement and wants to keep the level at 0.7% of GDP, Labour agree and will maintain that level.
In 2013, only five countries had met or exceeded the 0.7% aid spending target.
David Cameron has chosen not to debate and that has ruled the Liberal Democrats out too.
