The British High Commission says Nnamdi Kanu, leader of the Indigenous People of Biafra (IPOB), was not arrested in the UK.
The fugitive leader of the outlawed group was arrested on Sunday, according to the Attorney-General of the Federation, Abubakar Malami.
Malami had said Kanu was arrested through the collaborative efforts of Nigerian intelligence and security services.
However, he neither gave details of the operation nor stated where Kanu was arrested.
Since the IPOB leader was known to have stayed in the UK after he fled Nigeria, many had concluded that he was arrested in Britain.
Kanu is a dual citizen of Britain and Nigeria.