JOHN Swinney is set to become the latest leading politician to publish his tax return, sources close to the Scottish Finance Secretary have confirmed.

David Cameron’s assertion amid the tax row that prime ministers and chancellors should disclose their financial details because they were in charge of the nation’s finances prompted the question whether or not the Prime Minister believed Nicola Sturgeon and her deputy should also publish their tax returns, particularly as Holyrood is accruing more fiscal powers.

No 10 said Mr Cameron believed it was a matter for Scottish politicians what they did, noting how the First Minister as well as other party leaders north of the border had already published their tax details.

However, Mr Swinney, who last month floated the idea that, because Scotland was getting more powers, it might need its own chancellor, was conspicuous by his absence.

But last night, a senior source close to the DPM said he would be “happy to publish his tax return” and had not done so yet because he had been busy campaigning.

He added: “He's happy in principle and will publish.”

Lord Hague yesterday said an "age of greater transparency" would require more and more openness by public figures - on issues such as health as well as finances – but warned politics would be diminished if all of them were found to be squeaky clean.

The former Foreign Secretary suggested voters should not expect all politicians to be "perfect" or "normal", noting how Winston Churchill's tax affairs "would have been more difficult to defend in public than Prime Minister David Cameron's".

Meantime, Diane Abbott, the shadow international development secretary, made clear today that a future Labour government would stop using the services of the “Big Four” accountancy firms to deliver aid projects if they or their clients continued to use tax havens at the direct expense of the world’s poorest nations.

The party said the so-called Luxleaks scandal demonstrated how the Big Four – PWC, Ernst and Young, Deloitte and KPMG - were in the business of promoting international tax avoidance, which each year cost developing nations £140 billion; 50 per cent more than the total amount they received in aid from rich counties.

“There is a clear conflict of interest in DFID spending aid through these firms to reduce global poverty because these companies are themselves fuelling legal theft of the developing world’s public finances. This practice undermines development work,” declared Ms Abbott.

Meantime, George Osborne said Brussels plans to force multinational companies to be more open about their tax arrangements were "a step in the right direction".

But the proposals won only a lukewarm response from campaigners for tax transparency, who warned they could be "close to useless" unless they were extended to cover the whole world.

Under the scheme, large companies operating in the EU will have to publish the amount of tax they pay in each of the 28 member-states on a country-by-country basis, alongside details of their activities, number of employees, turnover and profits.

Crucially, they will also be required to produce a country-by-country breakdown of levies paid in states on a list of tax havens being drawn up by the EU.

The initiative is designed to put pressure on major companies to stop “profit-shifting” and pay tax in the countries where they make their money by making it easier for politicians and members of the public to judge whether or not they are artificially diverting profits to low-tax states.

Mr Osborne said the UK was leading the world in the fight against tax evasion as the EU move followed David Cameron's decision to put tax transparency at the heart of the UK's agenda for its presidency of the G8 in 2013.

"The Commission's proposals for public country-by-country reporting released are a step in the right direction towards new international rules for greater public transparency," said the chancellor.

John McDonnell, his Labour shadow, also welcomed the EU proposals but noted that while they had been supported by Labour MEPs, Conservatives in Brussels "were doing their best to block them".