Juncker came under pressure at the G20 summit in Australia over allegations he encouraged companies to take advantage of Luxembourg’s low tax rates, while he was finance minister and later prime minister.
Both Work and Pensions secretary Iain Duncan Smith and Tory party chairman Grant Shapps have encouraged the probe, giving further backing to Prime Minister David Cameron, who has fiercely opposed Juncker’s appointment.
Speaking on BBC Radio 5 Live, Duncan Smith said: “This is a real moment for the European Union, for the commission, to show that it has the capacity and the determination to investigate its own.”
Speaking on the same programme, Shapps said: “I haven’t seen all this evidence. I think it is absolutely right that it is properly investigated and that is what I hope will happen next.”
Juncker says all tax settlements reached under his leadership complied with national laws and international rules.