When Eton master Will Knowland was sacked last year over anti-feminist views contained in a YouTube video which he refused to take down, alumni and others rightly called out Eton’s small-mindedness and intellectual conformism. If the best-endowed schools in the land can’t stomach unorthodox opinion, what hope for UK education generally?

They were, of course, entirely right. But there is a further, more serious, side to the story. This week’s widely-welcomed victory by Knowland is not the end of the matter. Eton, as it was required to do when dismissing a teacher for gross misconduct, had reported the circumstances to the professional body for teachers, the Teaching Regulation Agency. The TRA was then obliged to consider whether to disqualify Knowland as a teacher completely, on the basis that his publicly-expressed views had brought the teaching profession into disrepute. It decided that Knowland’s case ‘should be closed with no further action’. As a result he is now free to teach at any school that will have him.

This is clearly excellent news. Nevertheless the affair shows that teachers – and especially those with unfashionable views – can still face a worryingly rough ride.

For one thing, the consequences of falling foul of the TRA are not trivial. A teacher sacked by one school over an expression of opinion can always look for another more tolerant employer: an important escape-route, given that the atmosphere in school staff-rooms can vary from the pompously prescriptive to the relatively easy-going. A teacher handed a prohibition order by the TRA, by contrast, is prevented by law from teaching anywhere in the UK, public or private; and since such prohibitions tend to last at least two years, this in many cases essentially amounts to deprivation of livelihood.

Furthermore, it’s not as if the TRA’s power to ban teachers was limited to the kind of thing that must unarguably disqualify anyone from the classroom: subversion of exams, sexual misconduct involving pupils, or whatever. On the contrary: the organisation’s remit is wide-ranging. It can adjudicate on and penalise any ‘unacceptable professional conduct’ or acts ‘that may bring the profession into disrepute’: matters which, as the Department for Education’s Teachers’ Standards guide puts it, include such vaguely-defined sins such as not treating pupils with dignity, or – importantly – saying anything seen as ‘undermining fundamental British values, including democracy, the rule of law, individual liberty and mutual respect, and tolerance of those with different faiths and beliefs.’

However lucky Will Knowland may have been, other teachers have indeed been disqualified for what they have said, even outside work. Earlier this year, for example, the Welsh equivalent of the TRA had little hesitation over banning a North Wales teacher for comments about conditions and behaviour in his school, even though neither he nor the school was named in his blog; and at about the same time, a Rotherham schoolmaster was served with a minimum two-year prohibition after expressing unfavourable views online about Islam and gay marriage.

Whatever you think of such behaviour, the difficulty is this: once we get beyond matters which ought to prevent anyone teaching anywhere, it is difficult to see how the interposition of the TRA in the licensing of teachers can be justified. Actual political indoctrination in the classroom is forbidden by law. But subject to this, schools vary in ethos and outlook. If a local authority, or a private school, wishes to employ a teacher with unconventional views or a loose tongue, then even if that person’s opinions are (say) undemocratic, or contrary to the rule of law, it should be up to it to decide whether to do so. It is no business of the law to prevent it.

Indeed, it gets worse. As long as we have laws requiring teachers to forfeit the right to teach unless they support things such as British values, or individual liberty, or the rule of law, then even taking into account Will Knowland’s victory last week there is a danger of quite serious censorship. Invoking ‘British values’, for example, can justify a good deal of suppression of opinion: indeed, in the case of the Rotherham teacher it was ‘British values’ that were ruled to have been undermined and this was deemed to be incompatible with a schoolteacher’s right to teach.

So too with holding a view which questions the rule of law: could this be used to inhibit criticism of, say, the European Convention on Human Rights? Or for that matter an argument in favour of abandoning the Northern Ireland protocol? And who is to say that criticism of populism is not an attempt to subvert democracy?

Of course we don’t know whether any of this will happen. In practice what sentiments are seen as incompatible with teaching the young may well depend on the mood and makeup of the particular TRA panel before which a teacher appears.

But for a teacher with any but the most orthodox views, the prospect of having to appear before such a panel – with the possibility of being banned from teaching for expressing a view which is both lawful and, as often as not, something that might appear in the pages of a national newspaper – is a powerful incentive to keep quiet and conform.

If we want our schools, both state and private, to be genuine sources of varied and pluralist thought, this is precisely the kind of influence we don’t need. For the sake of all our children, the power of the TRA over teachers needs to be permanently curbed.