It is 15 years since the US declared the “war on terror” and, while the rise of Islamic State has ensured western governments remain preoccupied with non-state armed groups, the international policy agenda has shifted towards a broader focus on countering “extremism”. But one problem with this is that there is no agreement on what “extremism” is, let alone its causes or solutions.

The question of what constitutes a terrorist has always been contentious; the definition of “extremism” is even more so. Just as countries around the world leapt to label their dissidents terrorists after 9/11, the UK’s growing emphasis on “nonviolent extremism” is ripe for exploitation by authoritarian governments.

Britain has gone further than most countries in defining extremism specifically as a problem of undesirable beliefs. When the coalition government came to power in 2010, it revised the Prevent strategy to define extremism as “vocal or active opposition to fundamental British values” including democracy, the rule of law, individual liberty and tolerance of different faiths and beliefs.

This change in policy was partly a reaction against some of the counter-terrorism work done by the previous Labour government in conjunction with Muslim faith groups. Critics claimed some of the faith groups that had been selected actually contributed to underlying problems of intolerance and division, because they reinforced the idea of separation between Muslim and other British communities. Moreover the new definition of nonviolent extremism was intended to be wider than Islamist groups, and to include the far right.

The definition, however, is not based on any clear theoretical or practical link to violence. Clearly, “nonviolent extremists” don’t have to be in favour of violence. The latest counter-extremism strategy, from 2015, states that extremist ideology is the core problem, with terrorism merely a symptom. By contrast, the research on terrorism, radicalisation and extremism suggests that, though beliefs matter to people and organisations who adopt violence, a more complex mix of social, psychological, political and strategic factors plays a part.

The idea of “non-violent extremism” has critics ranging from academics defending freedom of thought – such as Oxford University’s vice-chancellor this week – to police officers questioning how this concept could realistically be controlled.

But much less attention has been paid to the fact that Britain is also exporting its definition. Few people have analysed the implications for foreign policy of the UK promoting this concept of “non-violent extremism” among its global allies, through training programmes as well as high-level security dialogues. The concept hasn’t caught on with most western democracies, which remain focused on countering violent extremism; but it has been warmly received by non-democratic states, including some in the Gulf, which favour the sort of broad definitions that tar nonviolent dissidents with the same brush as violent ones.

Paradoxically, the UK’s definition of extremism is intended to reinforce liberal democratic values. But this is lost in translation when non-democracies embrace it. They are not amending their definitions to promote liberal values: rather, they tend to see Britain’s approach as validating their view that it is legitimate to criminalise dissident beliefs as a threat to national security.

When it comes to counter-terrorism cooperation with the Middle East, there is a clear common interest in fighting a recognised, common threat such as Isis or al-Qaida. By contrast, the understandings of what constitutes “extremism” are so far apart that proponents of democratic change – or of liberal social values, such as the freedom to be an atheist or to advocate LGBT or abortion rights – are viewed as extremists in the Gulf context.

Nor are Gulf states themselves united over what extremism means. The UAE and Qatar have opposite views on whether the Muslim Brotherhood is an extremist organisation, while Saudi Arabia’s grand mufti says Iran’s leaders are not Muslims. By contrast, the UAE has made it illegal to declare other Muslims to be apostates, as it sees this “takfirism” as deeply interlinked with extremists.

The UK, keen to strengthen its counter-terrorism partnerships, seems content to gloss over these differences. But if we don’t deal with the consequences of our loose definitions, including human rights abuses and the stoking of popular discontent in response, we could be storing up problems that come back to haunt us.