"Let's dive straight in," said presenter Cormac Ó hEadhra, as he kicked off the first radio presidential debate in which all of the candidates were in attendance. And 'straight-in' meant talking about spending and transparency at the Áras.

It's a topic which was going to put Michael D Higgins on the defensive, given the other candidates had been vocal in their criticism. But then the debate would shift to how the other five contenders were funding their campaign, and whether they had sufficiently distanced themselves from any commercial interests.

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On finances at the Áras, Independent candidate Gavin Duffy raised a general concern about the absence of detailed information. He said: "We don't know what anything at the Áras is costing... Anything that is shrouded in secrecy is not good for democracy."

Independent candidate Seán Gallagher went a step further when he expressed concern about "what would appear to be extravagance" at the Áras. He asserted: "We have heard stories about three thousand euro a night hotels", adding that this led to concern because finances at the Áras were "not fully transparent".

Another Independent candidate, Peter Casey, went further still with direct criticism of the incumbent: "I think that Michael is being totally disingenuous. You take a Learjet to go up to Belfast, for goodness sake. That's the sort of nonsense that should not be allowed."

Michael D Higgins pointed out that he didn't choose where to stay or how to travel when abroad on State business. He also said he wanted to reassure the public that "everything [at the Áras] has been properly managed".

The President said he was always open to being transparent. He said: "It's appropriate that we would have better procedures and I haven't the slightest difficulty with full compliance."

However, that didn't cut much ice with the Sinn Féin candidate Liadh Ní Riada: "This is something which should have been addressed at the beginning of the [Higgins] term - that you map out how you mean to go on. And I do think that accountability and transparency is key."

There appeared to be a consensus among all of the candidates that, when it came to finance, transparency could be improved.

Independent candidate Joan Freeman said: "I think that audited accounts - every single year - should be available for the public. By doing it that way, there is no need for conversations like this."

The debate didn't solely focus on finance - Liadh Ní Riada had a few cuts at Seán Gallagher, wondering what he had "been doing for the last seven years" since he last ran for the Presidency.

Seán Gallagher responded: "In 2011, I - like many people in this country - I started again. I pay my tax in Ireland. I'm fully compliant with tax."

In their comments afterwards, some candidates expressed the desire that future debates would focus on their platforms for the Presidency. However, it seems more likely that finance will remain a hot topic for the next two weeks.

Asked about a recent opinion poll, which put Michael D Higgins securing 70% of first preference voters, most of the other candidates repeated the mantra that "campaigns matter".

Seán Gallagher, though, had the best line. Speaking to reporters afterwards he said: "I am the living proof that unprecedented things can happen".

Let's see.