The SNP's lead candidate for the upcoming European election has said he is "agnostic" on the question of what currency an independent Scotland would use.

Alyn Smith made the comment as MEP candidates from six parties went head-to-head live on STV in a Scotland Tonight debate special ahead of the May 23 vote.

Smith was joined by David Martin from Scottish Labour, the Scottish Conservatives' Nosheena Mobarik, Scottish Greens co-convener Maggie Chapman, Sheila Ritchie of the Scottish Lib Dems and Jim Ferguson from the Brexit party.

Monday night's programme was presented by STV's political editor Colin Mackay, with a format that saw each candidate grilled in turn by their election rivals.

The Scottish nationalist MEP Smith was pressed on if he supported an independent Scotland using the Euro, and replied that he was "agnostic on the currency question".

He added: "I don't have a preference. My preference is what's best for the Scottish economy."

But at its most recent conference, the SNP endorsed a position that an independent Scotland should have an independent curreny "as soon as practicable".

Labour's David Martin, the party's lead candidate in Scotland, faced questions on Jeremy Corbyn's position on a People's Vote, while the Tories' Nosheena Mobarik said she would back "whoever" becomes next Tory leader - including Boris Johnson.

The Brexit party's third candidate on the Scotland list, Jim Ferguson, took tough questions from Smith and Maggie Chapman on funding for the new pro-Leave party led by Nigel Farage.

Chapman, the Green candidate, also clashed with the Lib Dems' Sheila Ritchie on the future of the oil and gas sector in Scotland.

In turn, Ritchie was challenged on her party's role as a junior partner in the former UK Coalition government and its austerity policies.

Ukip and Change UK did not feature in the debate but spoke separately to Colin Mackay, with Ukip's lead candidate Donald MacKay describing the new Brexit party as a "one-man band".

Change's lead Scottish candidate Peter Griffiths, who had to step in last week after the party's original top candidate defected to the Lib Dems, said his party did not "actually want to change anything in Scotland".

Smith opened the debate at the podium, with Mobarik asking the SNP MEP about views he had previously expressed in favour of an independent Scotland using the Euro.

"I'm agnostic on currency stuff and we've had within the SNP a lively debate about what sort of currency options there will be for an independent Scotland," Smith replied.

He added: "I think it's about what matters best for economic stability of our country, for long-term investment, people's pensions, people's homes.

"This is too important to just be a matter of ideology, this is about what works best."

The SNP candidate, first elected as in MEP in 2004, then took his turn to question Labour's Martin, who has been in the European Parliament since 1984.

Smith asked the pro-Remain Martin what could be done to "bring Jeremy Corbyn towards your position" on Brexit.

The Scottish Labour candidate answered that Corbyn "is coming round to the idea that we now have to go back to the people" with a second EU referendum.

Martin conceded: "I don't entirely agree with him but I understand why he had to take the position that he had to take."

Mobarik, meanwhile, was challenged repeatedly on if she would back Boris Johnson as PM but refused to be drawn.

The Tory candidate told Scotland Tonight: "I am backing whoever becomes Prime Minister... it is absolutely hypothetical at the moment who is going to be Prime Minister."

The Brexit party, whose lead Scottish candidate Louis Stedman-Bryce was unavailable to attend Monday's debate, faced scrutiny on where its money comes from.

Chapman pressed the party's third candidate Ferguson to confirm it is "not being funded by people who want to starve our public services of taxes.

The Brexit party candidate dismissed the question as "utter nonsense", adding: "We are not a party of wealth. The membership of our base, the grassroots, paid £25 for their membership...

"We are beyond a political party, Maggie, we are now becoming a political movement."

It comes after former PM Gordon Brown wrote to the Electoral Commission about online contributions the Nigel Farage-led Brexit party, as well as continued questions over the funding of Farage by controversial businessman Arron Banks.

Ferguson repeated his party leader's comments earlier in the week that any financial issues concerning Banks are "entirely a private matter".

Scotland Tonight also interviewed Ukip and Change UK's lead Scottish candidates Donald MacKay and Peter Griffiths.

MacKay told the programme that economic warnings about a no-deal Brexit were "doom and gloom".

He said: "This is the millennium bug syndrome: everything's going to stop, everything's going to fall apart, if we don't join the Euro, everything's going to fall apart. It didn't...

"The biggest obstacle we've got to expanding and growing is government, and in particular, the EU."

Griffiths, standing for Change - the party which formed after 11 MPs broke away from Labour and the Tories to form a new independent grouping - said his party was explicitly anti-Brexit.

"Brexit is stopping absolutely everything in this country," he said.

"We've seen three years, no progress on anything, it's stagnating our business, it's causing disruption to our services, and it needs some change."

But he added: "We don't actually want to change anything in Scotland, we want to change the United Kingdom."