Boris Johnson, Britain's recently-resigned foreign secretary, built his political career by courting controversy. He has gained notoriety over the years by referring to young women as "hot totty", gay men as "tank-topped bumboys" and black Africans as "piccaninnies".

His latest foray into populist obnoxiousness came earlier this month with a newspaper column which ridiculed Muslim women who wear the face veil as looking like "bank robbers" or "letter boxes". 

His column was prompted, ostensibly, by a new law in Denmark which bans people from covering their face in public. Though the law is not explicitly directed against Muslim women who wear the niqab or burqa, it's obvious they will be the people most affected by it.

Johnson went on to say the Danish law was a mistake and he didn't want to see a similar law in Britain – though he thought there were situations where faces should be uncovered. Employers, for example, should "be able to enforce a dress code that enables their employees to interact with customers".

Other British politicans have said similar things in the past, including the former Labour cabinet minister Jack Straw, and Johnson's column would probably not have attracted much attention without the gratuitous references to letter boxes and bank robbers. They added nothing to the points he was making and, on past form, it's safe to assume he was being deliberately provocative to keep himself in the limelight.

The face veil is controversial, even among Muslims, and many of them would agree with Johnson that it's a symbol of female oppression. Worldwide, only a minority of Muslim women wear it; it's not prescribed by the Qur'an and on any sensible interpretation of Islamic teaching isn't a requirement. The scripture simply urges Muslims – male or female – to dress modestly and not to flaunt themselves in the way they dress.

A Muslim woman who chooses to wear the face veil of her own free will is making a public statement about herself and her religion: she is not only showing that she is Muslim but is displaying her allegiance to a socially regressive version of Islam. But whatever negative feelings that might generate in others, she still has rights. She is entitled to her religious views, reactionary as they may be, and by walking in the street with her face covered she is not actually harming anyone.

In principle, religions and related social practices should not be off-limits for discussion and criticism, though a lot hinges on the way it is done. One particular danger is that it can be exploited by those with other agendas, especially on the far right where complaining about cultural “markers” such as religion, language or dress has increasingly become a substitute for more explicit forms of racism. 

In the hands of racists, the face veil is one of these markers, not least because it is so noticeable and culturally distinctive. As an example of women's oppression, though, it's relatively trivial. There are plenty of more serious things in that area to be concerned about – such as forced marriages, gender segregation and female genital mutilation – but the face veil is the one most likely to arouse the rabble.

Not surprisingly, since Johnson's column appeared there has been a sudden increase in incidents involving Muslim women wearing the niqab or even a simple headscarf, according to Tell MAMA, an organisation which monitors attacks on Muslims. 

Making fascism respectable

As a campaigning atheist, Richard Dawkins dislikes Islam and often exercises his right to say so. Besides taking generalised swipes at “the menacing rise of Islam”, he has said “It is well arguable that Islam is the greatest man-made force for evil in the world today”, and “If you see a Muslim beating his wife, there would be little point in calling a policeman because so many of the British police are terrified of being accused of racism or ‘Islamophobia’.”

In saying this, Dawkins – a distinguished emeritus fellow and former professor at Oxford University – sounds remarkably like Nick Griffin of the far-right British National Party who said in one of his speeches: “This wicked, vicious faith has expanded from a handful of cranky lunatics about 1,300 years ago till it’s now sweeping country after country before it, all over the world."

The problem here is that broad-brush critiques of the kind apparently favoured by Dawkins help to make the extreme right seem more respectable. One well-known American atheist, Sam Harris, has even gone so far as to say that “the people who speak most sensibly about the threat that Islam poses to Europe are actually fascists”.

When religion isn't sacred

Meanwhile there are those who argue that religions – uniquely – should have a protected status where criticism is concerned. Numerous Muslim countries have laws against "defaming" religion and according to a declaration issued by the Islamic Council of Europe no one should be allowed to “hold in contempt or ridicule the religious beliefs of others”.

On the other side of the argument, a UN study which sought to draw boundaries between free speech and hate speech noted that the right to freedom of religion or belief "does not include the right to have a religion or a belief that is free from criticism or ridicule".

In a similar vein, a landmark ruling from the European Court of Human Rights in 1976 said the demands of pluralism, tolerance and broadmindedness are so great – at least, in democratic societies – that freedom of expression should be protected even when it causes offence. It ruled that freedom of expression applies not only to ideas “that are favourably received or regarded as inoffensive or as a matter of indifference, but also to those that offend, shock or disturb the state or any sector of the population”.

The need for this provision is easy to see, because without it anyone would be able to silence free speech simply by claiming to have been offended, shocked or disturbed. But having a right to offend doesn't mean it's OK to offend people just for the sake of it. The court went on to say that people who exercise their freedom of expression also have "duties and responsibilities".

In 2008, a study by the Venice Commission (under the auspices of the Council of Europe) elaborated on this point:

"Since the exercise of freedom of expression carries duties and responsibilities, it is legitimate to expect from every member of a democratic society to avoid as far as possible expressions that express scorn or are gratuitously offensive to others and infringe their rights."

It must be possible to criticise religious ideas, the commission said, "even if such criticism may be perceived by some as hurting their religious feelings". It added that "an insult to a principle or a dogma, or to a representative of a religion, does not necessarily amount to an insult to an individual who believes in that religion". 

The commission acknowledged that the dividing line between insulting speech and incitement to hatred is “often difficult to identify”. Relevant factors include the intention of the accused speaker or author, the effects of his or her action, the context in which the statement is made, the intended audience and whether the statement was made by someone acting in an official capacity.

On the question of race and religion, the commission accepted – up to a point – that "a wider scope of criticism" might be acceptable in connection with religion but said it should not become an excuse to stretch the boundaries between “genuine ‘philosophical’ discussion about religious ideas and gratuitous religious insults”.

The word “gratuitous” appears several times in the commission’s report, and it can be quite a useful test for unacceptable speech. Applying that to Johnson's column, it's a test that his references to letter boxes and bank robbers clearly failed.

• For further discussion of this, see "The right to offend, shock and disturb" and "Atheism and Islamophobia" – chapters in my book, Arabs Without God.