More than eight million people tuned in to watch Nick Griffin on Question Time last night - around three times the usual number of viewers and just over half of the potential audience.
The BBC has defended the BNP leader's appearance, in which he gave a twitchy performance and described homosexuals as "creepy".
Hundreds of angry protesters massed outside Television Centre in west London last night as Mr Griffin also denied he was a Nazi and said the Ku Klux Klan were "almost totally non-violent".
The BBC came under fire from critics who accused it of legitimising the BNP's "racist" policies by inviting Mr Griffin on to the show.
The corporation said that average viewing figures for the programme are between two and three million - meaning three to four times more viewers tuned in than usual.
Mark Byford, deputy director general of the BBC, said today: "Over eight million people watched Question Time last night.
"This very large audience clearly demonstrates the public's interest in seeing elected politicians being scrutinised by the public themselves.
"The agenda of the programme was set by the audience's own questions.
"The BBC is firm in its belief that it was appropriate for Mr Griffin to appear as a member of the panel and the BBC fulfilled its duty to uphold due impartiality by inviting him on the programme."
The show drew an audience share of just over 50 per cent.
Media regulator Ofcom said it is considering several complaints about the programme. A spokesman said: "A small number of complaints are being assessed against the Broadcasting Code."
Ofcom regulates issues of harm and offence in BBC broadcasts but questions of impartiality and inaccuracy are the responsibility of the corporation's governing body, the BBC Trust.
The regulator will not release precise figures for the number of complaints until Wednesday next week.Reuse content