The familiy of Patrice Lumumba, the assassinated first Prime Minister of Congo, have demanded an apology from the Fine Gael leader Enda Kenny, who called the revered African liberation hero a 'nigger' in a racist joke.

Disgust at Kenny's recent remarks spread last night to Britain, where he was condemned by race campaigners, including the powerful Commission for Racial Equality watchdog and British political parties.

In a remarkable twist, The Observer has discovered that members of Lumumba's family - including one of his six sons and seven of his grandchildren - are living in Tallaght in west Dublin, after fleeing political persecution in the former Zaire in 1997.

Kongole Lumumba, son of the murdered leader, told The Observer of his hurt and embarrassment on learning of Kenny's remarks from his 15-year-old son, who was told of them at school last week.

He now wants the Fine Gael leader to explain his actions. 'Mr Kenny made a public apology, but he didn't apologise to me.' He added: 'It is very sad to hear of my father, who was a great man, being spoken about in this way. I would like to call that man [Kenny] and ask him exactly what he was talking about. I still can't believe that a man in his position would make such a remark. He has made a spectacle of himself.'

Anti-racist groups in Ireland and Britain are dismayed that Kenny has been able to keep his job after his comments about Lumumba, the first leader of an independent Congo, who was assassinated by opponents in 1961.

Fine Gael officials in Dublin have attempted to dismiss the issue as 'dead', but critics have been dismayed by the party's attitude and the lack of public debate about the issue. Prominent supporters, including Lord Henry Mountcharles, have also expressed their anger.

Campaigners in Britain said such words would result in instant dismissal. The Conservative Party leader, Iain Duncan Smith, sacked front-bench agriculture spokeswoman Ann Winterton earlier this year after she told a racist joke at a function.

A Tory spokesman said: 'It happened in the Tory party to a lesser degree and it's quite clear how we dealt with it. I don't understand why Fine Gael have not done the same. Politicians need to be careful about what they say.'

Kenny made the remarks at a private function in Dublin during a speech to party workers and journalists earlier this month. During an anecdote about a holiday in Portugal, he said a Moroccan barman 'with shiny teeth' had been asked why a cocktail was called a 'Lumumba' and replied it was named after 'some nigger who died dans la guerre'.

Kenny initially asked reporters at the function not to report his remarks and, to the astonishment of some commentators, a number of newspapers agreed. The Irish Sunday Independent, however, reported the story, and last week Kenny admitted he was wrong to have used the words and claimed his party was 'committed to diversity'.

In London, a spokesman for the Commission for Racial Equality said it was 'inconceivable' that a prominent politician in Britain would use such language and keep his or her job. 'Over the last two years there has been an enormous amount of concern about racist attacks in Ireland, and the government has enacted far-reaching legislation on equality and racial hatred. Clearly public opinion and the Fine Gael leader have some catching up to do.'

In a statement, Kenny told The Observer last night: 'The fact is that I used the word, and no context can excuse it. I failed to exemplify my own standards and those of my party. I apologise for any offence this may have caused, particularly to the Lumumba family.'

Lumumba's 15-year-old grandson, Joseph, said he first heard of the controversy when his teacher pulled him aside last Monday morning. 'I just couldn't believe it. You expect to hear that word on the streets, but you wouldn't expect it of someone of his stature.'

The London-based Refugee Council joined its Irish counterpart in condemning the remarks, saying they could damage race relations in a country where attacks on asylum seekers are on the increase: 'Politicians have a duty to set an example to the public. They must ensure that the tone and language they use when talking about sensitive issues enhances and fuels the debate,' a spokesman said.