Williamson also said he believes no more than 300,000 Jews died in Germany's Nazi concentration camps.
The number of those killed in the Holocaust that is widely accepted is six million people.
Last week, the Argentine government gave Williamson 10 days to leave the country after his views "deeply shocked Argentine society, the Jewish people and all of humanity".
Argentina has one of the world's largest Jewish populations outside of Israel.
Williamson, a member of the Saint Pius X Society, headed a seminary near Buenos Aires until earlier this month.
Christian Bouchacourt, a senior official for the society, said he did not know what Williamson had planned for the future.
"I don't know anything at all. That now depends on him and his superior general [a senior Catholic official]," he told the AFP news agency.
"I think it will all be done discretely and kept 'in the family'."
Holocaust denial is not a specific offence in Britain, and the country's interior ministry has not commented on the case.
Last month, Pope Benedict, the head of the Roman Catholic church, angered Jewish leaders and many Catholics by lifting the excommunication of Williamson and three others in a bid to heal a 20-year-old schism within the Church.
The schism began in 1988 when the four were ordained without Vatican permission.
World Jewish organisations and Angela Merkel, the German chancellor, have criticised the pope for rehabilitating Williamson.
The Vatican later ordered Williamson to retract his comments, but Williamson said he needed more time to review the evidence.