Was this a great day for democracy, I was asked this morning as I sought for the umpteenth time on television and radio to justify the BBC’s decision to invite the BNP onto its Question Time programme. Of course it is not a great day when a party that is avowedly hostile to ethnic minorities is given a platform on the broadcaster’s most prestigious discussion programme. This is not a day that will be remembered with fondness by anyone except supporters of the far-right party.

And yet the alternative for democracy and for free speech – the most basic of civil liberties – would have been worse. The most important free expression is the right of an individual or organisation, whose views one finds most obnoxious, to have its say. One works from the assumption that Nick Griffin, the BNP leader, will be subjected to robust, passionate and forensic cross-examination. The rest is up to the good sense of the public.

The only realistic and practical criteria for curbing free speech reside in the law. If Griffin or any of his followers break the law – as they have done in the past – then they should be subjected to the full might of the law. Until or unless they do, they are entitled to be heard no matter how uncomfortable that leaves mainstream society.

It is not for governments, less still public service broadcasters, to determine the acceptability of opinion. When in February Jacqui Smith, the then Home Secretary, announced a list of 16 undesirable foreigners who would be denied access to the UK – from the Dutch far-right politician Geert Wilders to radical Islamist preachers to an American shock-jock radio host – she was setting a worrying precedent. One is either a free individual or guilty of a crime. That is surely one of the most important lessons of our, imperfect, democratic system.