Hundreds of people attended a neo-Nazi rally that was not opposed by police in the belief it was a charity event.
About 350 people attended the rally on the anniversary of the death of Ian Stuart Donaldson, who founded white supremacist group Blood and Honour.
But Cambridgeshire Police said the force had been told the Haddenham gathering on 23 and 24 September was in aid of Help for Heroes.
Mr Donaldson died in a car crash in Derbyshire in 1993, aged 36.
Blood and Honour has been banned in a number of countries across Europe and in Russia.
Matthew Collins, from the Hope not Hate campaign group, told the BBC the gathering was an annual Blood and Honour event following the death of Mr Donaldson and had moved around the UK because it had “struggled to find venues that will host them”.
He said there were a number of banning orders against the group in other countries due to imagery used at concerts and links to violent extremism.
About three-quarters of those attending travelled from Europe to be at the event and this included people from countries that ban Blood and Honour.
A witness to the event, who wished to remain anonymous, described seeing “a lot of cars, a big bonfire and a lot of music”.
“The one that I heard was a song about white power and this kept going on and on. It was very loud and distinctive.”
East Cambridgeshire District Council said a temporary event notice was filed online for a “private party with music”.
It said, like all applications, it was passed to the police to see if they had any objections and, as none were raised, the event went ahead.
Help For Heroes said the event was not registered with the charity, adding it was “strictly non-political” and it did not accept donations from extremist groups.
Mr Collins said it was “disappointing” the event had been allowed but he was “aware of a number of occasions when the police appear to have been caught short about the activities of the extreme far right”.
Mark Gardner from Community Security Trust, which protects British Jews from anti-Semitism, said it looked “like somebody pulled the wool over the police’s eyes”.
The BBC contacted Blood and Honour for comment.