Clarke attacks his rival as a 'hanger and flogger'

The Tory leadership battle descended into the bitterest personal clashes of the campaign yesterday when Kenneth Clarke accused Iain Duncan Smith of being a right-wing "hanger and a flogger".

Mr Clarke said his opponent was closely connected to extreme pressure groups and called him "the epitome of a right-wing Tory".

The controversy over Mr Duncan Smith's racist supporters showed no sign of abating as the contenders faced questioning on BBC Radio 2's Jimmy Young Show.

Mr Duncan Smith was challenged on the revelation that one of his activists, who has since been sacked by the campaign, was a British National Party sympathiser and that some of his supporters backed the voluntary return of immigrants to their country of origin.

Mr Duncan Smith is expected to face further criticism from ethnic-minority campaigners today over his failure to sign a Commission for Racial Equality compact before this year's general election. The pledge included a promise not to use racially inflammatory language during the election campaign and not to do anything to undermine ethnic minority groups in Britain.

Mr Clarke was among the 520 MPs to have signed the promise, but Mr Duncan Smith abstained.

Yesterday Mr Duncan Smith dissociated himself from advocates of the voluntary repatriation of immigrants and denounced the BNP and its policies. "I have had to fight these people and I think that what they stand for is wrong," he said.

He insisted that he was not right-wing, and said that the contest had become "obsessed with this rather Westminster-based concept.

"Whenever I'm asked about this so-called concept of right-wing and left-wing I just don't understand it," he said.

Meanwhile Mr Duncan Smith has overtaken Mr Clarke as the contender most favoured by Conservative voters, according to a poll published last night.

A Mori poll conducted for The Times found Mr Clarke remained the preferred choice of voters as a whole, and the candidate Tories believed would stand the best chance of winning round the country, but indicated that Mr Duncan Smith has built momentum during the campaign and has been closing the gap on his rival.

The poll found that 41 per cent of Conservative supporters backed Mr Duncan Smith, compared with 36 per cent for Mr Clarke, reversing the position in a similar poll last month. Some 40 per cent of Tory voters believed Mr Duncan Smith would be best at uniting the party, compared with 34 per cent for Mr Clarke, again reversing the situation of a month ago. But Mr Clarke was ahead when Conservative supporters were asked which candidate would increase the party's support across the country, by 42 per cent to 37 per cent. Voters as a whole, however, backed Mr Clarke on all three questions.

Mr Clarke faces further questions over his links with British American Tobaccoafter the disclosure that he had approved the promotion of an executive whose activities are to be investigated in a smuggling inquiry.

His judgement as deputy chairman of BAT was questioned because he decided to approve the appointment of Paul Adams as the company's managing director. Mr Adams is named in internal documents that imply the company was involved in cigarette smuggling in South-east Asia, although there is no suggestion that Mr Adams was involved.

The documents are to be sent to Patricia Hewitt, the Secretary of State for Trade and Industry, this week as part of an investigation into BAT's involvement in international cigarette smuggling.

Mr Clarke defended his role at BAT and denied reports that the company directed its advertising campaigns towards children.