The leader of the BNP, Nick Griffin, found himself the victim of an extraordinary attack from his own supporters last night following his controversial appearance on the BBC's Question Time.

As a public postmortem into one of the most divisive broadcasts in the corporation's history attempted to gauge its impact on the party's fortunes, Lee Barnes, the BNP's legal officer, accused Griffin of "failing to press the attack" during the televised debate, which was watched by a record 8 million people. Others sympathetic to the BNP's views expressed dismay at Griffin's flustered attempts to appeal to the mainstream.

The BNP's critics were quick to use the comments as proof of deep divisions within the party's membership over how it should position itself with the electorate. Griffin has claimed that he has dragged the party into the political mainstream. But the resulting backlash from those on his own side suggests many are uncomfortable with the BNP's attempts to cloak itself in more moderate terms.

Barnes complained on his personal website that Griffin "should have stood up to these whining, middle-class hypocrites that use the race card for self-enrichment – and thrown the truth right back into their fat, sanctimonious, hypocritical, self-serving faces". He accused his party's leader of "failing to press the attack" on the "ethnic middle class" for "taking up the best jobs while still playing the bogus race card for every opportunity". And in a move that is likely to reinforce concerns that Griffin's appearance will spark violence, Barnes used his personal website to suggest that "perhaps there needs to be a few 'white riots' around the country a la the Brixton riots of the 1980s before the idiot white liberal middle class and their ethnic middle-class fellow travellers wake up".

A spokesman for the anti-fascist organisation Searchlight said: "This strips away once and for all Nick Griffin's pretence that the BNP is a non-violent organisation. Lee Barnes is not just another BNP member, he is the organisation's legal officer, and here he is talking about riots in the streets. The BNP hoped the Question Time appearance would mark their entry to the political mainstream, but instead they have pushed themselves back to the violent, extremist political fringe where they belong."

Labour MP Jon Cruddas said: "If this is the view expressed by Griffin's legal officer, imagine the views among the hardcore BNP membership."

Griffin's performance on Question Time, in which he was ambivalent about incendiary comments he had made in the past, admitted to links with the Ku Klux Klan, attacked Islam and appeared sweaty, smirking and evasive, has been widely derided in the media and by politicians from all the main parties. But the party's sympathisers are also joining the attack. Negative comments from BNP supporters were posted on the party's website yesterday, but many were quickly taken down.

One comment read: "Maybe some coaching could of been done so that Mr Griffin could of answered any questions articulately."

And in far-right internet chatrooms, the mood last night was one of a missed opportunity. In the Stormfront online forum, a BNP sympathiser said: "It was quite a bad performance by Griffin in comparison to his other TV appearances. Though he managed to get one or two things over (despite the constant interruptions and barracking) that would appeal to the majority, he did seem overawed by the occasion and was not, for the most part, at his best."

Another said: "It's almost like Nick went on expecting a normal episode of Question Time, it was always going to be a hatchet job and he should have been fully prepared for questions relating to his past. This lack of preparedness left him open to attack and flustered when asked to provide a reply." Another commented: "I'm starting to think this appealing to the mainstream approach is the wrong direction. I would rather have seen George Lincoln Rockwell [founder of the American Nazi party] on the panel, there would have been a riot."

The emerging splits within the BNP's core support over Griffin's performance came amid claims that Question Time had acted as a recruiting agent for the far-right party. A poll for the Daily Telegraph published yesterday suggested that 22% of the electorate would "seriously consider" voting BNP, while the party claimed thousands had registered for information following Griffin's appearance. "By the end of the night 9,000 new people had signed up as registered potential members or on our mailing lists," Simon Bennett, the BNP's webmaster, declared. "In the Euro elections, we gained 40,000 enquiries, but spent £500,000 to do so – on Question Time we spent peanuts but gained almost 25% of the Euro election total in eight hours! We had to upgrade our server capacity enormously, which allowed us to cope with extra traffic."

The claims seemed to reinforce concerns expressed by the Welsh secretary, Peter Hain, who had opposed Griffin's appearance on Question Time. "The BBC has handed the BNP the gift of the century on a plate and now we see the consequences," Hain said. "I'm very angry."

The BNP – and indeed the entire far-right movement – is no stranger to infighting and claims of splits will be dismissed by its high command. Griffin, a former key player in the National Front, assumed control over the party only after ousting its founder, John Tyndall.

Since then he has shored up his position, surrounding himself with a core of lieutenants and taking control of party finances. This has led to concerns that Griffin has become too powerful. Several senior BNP members quit after he overhauled the constitution to make his position as leader practically unassailable.

In far-right chat rooms yesterday many were asking whether the Question Time appearance was a watershed. "Griffin carries too much baggage to act as spokesman for the BNP," one said. "I lost count of the number of times past quotes came back to haunt him."