Recent claims that the Luxembourg tax authorities exploited complex loopholes to strike secret deals with multinationals to minimise their tax exposure while Junckers was in charge, have given rise to charges of a conflict of interest.

Juncker, who spent two decades as Luxembourg’s finance minister and prime minister, took over the presidency at the beginning of November for a five-year term and announced his intention to ensure the EU took steps to crack down on tax avoidance.

Yesterday saw a specially-convened session of the European parliament debate the so-called ‘Lux Leaks’, which are based in part on 28,000 pages of documents from PwC covering tax deals Luxembourg agreed with some 340 multinationals during Juncker’s time in office, allowing the companies concerned to save billions of pounds of tax.    

Speaking to MEPs, Juncker  said that the tax rulings in Luxembourg were not illegal, even though he admitted that ‘there probably was a certain amount of tax avoidance in Luxembourg, as in other EU countries. We find this everywhere in Europe because there is insufficient tax harmonisation in Europe.’

‘When it comes to the application of different tax rules, often diametrically opposed, that can lead to results that are not line with ethical and moral standards. If there is insufficient tax harmonisation in Europe then this can be the result. In the course of my life I have sought greater tax harmonisation,’ Juncker said.

Juncker went on say that  Commissioner Moscovici, who handles taxation, will be initiating proposals for an automatic exchange of information regarding national tax rulings. He also stated: ‘This Commission will fight tax evasion and tax avoidance. This is not just words. This is very much the intention.’

Competition commissioner Margrethe Vestager is to investigate Juncker’s role in the development of preferential tax deals in Luxembourg in the light of the recent revelations. This is an extension of an investigation she is already conducting into tax schemes in Luxembourg, the Netherlands, Ireland and other EU countries, which include scrutiny of tax arrangements by Apple, Starbucks, Amazon and Fiat.

Juncker has sought to maintain that Luxembourg's tax authorities were independent of the government and denied having a central role in policies which saw global companies such as PepsiCola, Amazon and  Deutsche Bank benefiting from tax deals.

During the debate UKIP MEP Paul Nuttall said: ‘Mr Juncker, when you were campaigning during the European elections you stood on a platform of fighting tax evasion by multinationals but indeed you allowed that tax evasion in Luxembourg.

'Citizens are sceptical, because you want them to “do as I say, not as I do”. You have only two options: either to resign or to stand down while the investigation takes place.’