When David Miliband read the JC last Friday, he blew a gasket.

The cause of his fury was the interview with Michal Kaminski, Polish MEP and leader of the Tories’ new allies in the European Parliament, the European Conservatives and Reformists.

He had read Mr Kaminski’s frank remarks about his refusal to apologise for the notorious massacre of Jews at Jedwabne in July 1941 and his view that he did not judge this atrocity as being on the same scale as other crimes of the Holocaust.

Earlier in the week, Mr Miliband had been reminded of his own Polish-Jewish roots after his brother, Climate Change Secretary Ed Miliband was reunited with a long-lost relative during a radio interview in Russia.

The Foreign Secretary had a busy weekend ahead, with the visit of US Secretary of State, Hillary Clinton. Afghanistan and Northern Ireland were on the agenda, but Mr Miliband immediately put pen to paper to respond to Mr Kaminski in the pages of the Observer.

I did wear the Chrobry sword symbol on my lapel on occasions

Invoking Britain’s wartime fight against fascism, he said: “There will be incredulity in Washington, Beijing and Delhi, never mind Berlin and Paris, that a party aspiring to government in Britain — the party of Winston Churchill, no less — chooses allies like this.”

As the JC reveals today, Mrs Clinton’s visit coincided with growing concern in US diplomatic circles about the Conservative Party’s new partners in Europe.

The American administration now realises there is a very real possibility of a Conservative government next year and is concerned that the Conservative Party’s new alliance within the European Conservatives and Reformists (ECR) will hamper the UK’s ability to fulfil its traditional role as a transatlantic bridge between the EU and Washington.

At the time of his latest intervention, Mr Miliband had been under fire from the Tories for over a week about using his speech at Labour Party conference to attack Mr Kaminski’s “antisemitic, neo-Nazi past”. The interview, we are told, made him all the more determined to stick to his guns.

In his interview, the Polish politician reiterated his public opposition to antisemitism and his commitment to the state of Israel.

But he also said the following about the Jedwabne massacre, which was carried out by Poles against their Jewish neighbours: “I think that it’s unfair comparing it with a Nazi crime, and putting on the same level as the Nazi policy.” It is this refusal to recognise the full scale of the crime that caused Mr Miliband to re-enter the fray.

Further details of Mr Kaminski’s past emerged during the course of the week. Immediately following the interview, the ECR were forced to issue a clarification of their leader’s position on the wearing of the Chrobry Sword, a symbol of the Catholic ultra-right in Poland. During our exchanges Mr Kaminski denied that he ever wore the symbol, which was used by the antisemitic National Radical Camp Falanga Group in the 1930s.

However, a follow-up statement from Mr Kaminski, issued after the JC went to press, said: “I did wear the sword, which was used around a millennia ago to crown Polish kings, on my lapel on occasions.”

He added that after 1989 it was one of the symbols of the conservative Christian National Union party and worn by many mainstream right-wing politicians.

“In recent years it has been taken as a symbol by the far Right. Although it is not the same, there are similarities with how the BNP in Britain has taken the Union Jack as their symbol. When I felt the symbol started having this meaning I stopped wearing it and I asked the rest of my party to stop too.”

At the same time, evidence emerged of links between Mr Kaminski’s Law and Justice Party and a Polish radio station accused of spreading antisemitism.

Earlier this week, Denis MacShane MP, chairman of the European Institute for the Study of Contemporary Antisemitism, released a list of members of the ECR grouping who appeared on Radio Maryja.

In 2006, Marek Edelman, the last surviving leader of the 1943 Warsaw Ghetto uprising, who died this week, urged the government to close down the radio station because of its “xenophobia, chauvinism and antisemitism”.

Mr Kaminski himself has appeared as a presenter on the station on only one occasion, but others in the European grouping, including presidential hopeful Zbigniew Ziobro, have fronted dozens of the station’s programmes.

In public, the Conservative position on Mr Kaminski has hardened. Senior Tories have continued to back their leader’s line that there is nothing to hide about their new ally’s past.

However, behind the scenes, there is real concern that Mr Kaminski could still cause serious embarrassment to David Cameron. They know that the Tory leader has staked his reputation in Europe on this controversial man.