Following the verdict in Ali Harbi Ali’s trial on Monday, we must all now acknowledge what was clear from the outset: the murder of my friend and colleague Sir David Amess was an act of terrorism. More specifically, it was the product of Islamist extremism which this country – and the West – continues to face more than 20 years after 9/11.

Yet in the immediate aftermath of Sir David’s murder much of our political and media class entered into a worthy but spurious debate about the tenor of political discussion in this country, particularly online. Even after the police detained Ali under the Terrorism Act, many were unwilling to countenance extremism as his motive.

Instead of discussing the Government’s counter-terrorism strategy, we debated removing online anonymity and implored one another to be kinder – as if we bore some responsibility for the actions of this despicable murderer.

We cannot possibly hope to tackle extremism if we keep failing to diagnose it or, worse still, if when we do recognise it we pretend it is something else and reach for warm words and hashtags.

In its most dangerous form, this twisted ideology poses a direct threat to life. Despite a disturbing rise in far-Right extremism, Islamist radicals still make up the vast majority of suspects on MI5’s terror watchlist. And there remains a less violent but more pervasive strand of Islamist thought interwoven in our communities that needs stamping out.

It should be a continual source of outrage that a teacher from Batley Grammar School remains in hiding to this day, fearing for his physical safety, after showing depictions of the Prophet Mohammed in a religious studies lesson.

In recent years, we have become accustomed to cultural extremism – be it the divisive community politics in Tower Hamlets or the Trojan Horse controversy in Birmingham – which serves as a petri dish from which more violent forces can grow. In each instance, fear of political correctness or of causing offence has weakened the fight to defend sacred liberal principles.

Open societies such as ours should not be taken for granted. We have to constantly renew our battle against those who seek to undermine our values.

Two decades of recommendations and reports have equipped us with the solutions needed to grip this issue. Back in 2011, David Cameron outlined a less tolerant and more muscularly liberal vision for tackling hate groups; in 2016, Baroness Casey produced a persuasive report on the need for greater social integration which remains largely unimplemented; and as communities secretary I appointed Sara Khan (who also produced important and unimplemented recommendations for the Home Office on toughening the criminal law) to see how we can better protect the victims of extremism – like that teacher from Batley – whose fate we too often neglect.

It’s clear that Prevent, the Government’s counter-radicalisation strategy, needs urgent reform. In Ali’s case, he had been correctly referred to the programme but only went to one meeting and, despite continuing to be radicalised online, Prevent concluded he did not pose a significant danger and closed his case. This fits into a wider pattern.

Of the 11 most recent terrorist attackers, six had been referred to Prevent. And while the far-Right and Islamist extremists may despise our values in equal measure, it is irresponsible to draw equivalence in the cumulative threat their ideologies pose. Islamist extremists make up three quarters of offenders in prison for terror-related crime but only 24 per cent of all Prevent referrals and 30 per cent of Channel cases, that is those taken to the next level of intervention.

If Prevent is to succeed it must be focused on the greatest risk to life, without fear of appearances. It cannot afford to be passive and it needs to place the police and the security services in the driving seat.

We are doing the victims of extremism a colossal disservice by glossing over what really happened and failing to embark on the serious and sustained programme of work required to address it. Extremism of any kind, and certainly Islamist extremism, is a cancer that grows in our society. We must acknowledge it and summon the strength to fight it.

Robert Jenrick MP is a former communities secretary