An official working at the American Mission to the European Union has been anonymously altering the UK Independence Party entry on the online encyclopaedia, Wikipedia.
The changes, called "stealth edits", are in every case negative, underplaying the party's success and exaggerating its failings. They took place in July of this year and were revealed by a French blog, La Lettre Volée.
UKIP leader Nigel Farage MEP said: "I have written to the American Ambassador in the strongest terms to protest at this underhand behaviour. Though I am sure that this is not official US policy, it is symptomatic of the dishonest way in which the UK Independence Party is treated".
Mr Farage has requested a meeting with the Ambassador to ensure that this cannot happen again.
The US Mission has already launched an internal inquiry.