When it comes to achieving diversity among the upper echelons of management in Britain’s blue chip companies, there’s certainly an argument that progress is worth celebrating, however small and sluggish. And in this case you may even argue that progress has, in fact, not been small at all. At the end of last year, 40 per cent of CEOs of FTSE 100 companies were non-UK nationals. That marks a near doubling from 2001 levels, according to research from head hunter Odgers Berndtson published this week. The prestigious crowd of those in charge comprised 20 nationalities at the end of last year, which is up from just a dozen in 2001. Other top roles have also seen a sharp rise in non-UK nationals since 2001: almost 30 per cent of FTSE 100 chair people and CFOs are now non-nationals. And even on an international scale, the UK seems to be faring reasonably well. Of the 37 heavyweight French companies that Odgers Berndtson analysed, more than 86 per cent of CEOs were French, and in Germany 75 per cent were German nationals. But before we start championing the UK as a country of corporate multiculturalism, and patting ourselves on the back for achieving a veritable mosaic of ethnic diversity in our C-suites, here are a few sobering things to know. First of all, much of the trend toward more international boards in the UK has happened as a result of foreign companies deciding to list in Britain. Fundamentally, diversity has largely happened as a function of what companies from abroad are deciding to do, rather than a concerted domestic effort to become more worldly and international. And yes, you guessed it, Brexit-lurking just around the corner-could now threaten that fragile trend. Depending on how trade negotiations with the US, the rest of Europe and Asia pan out, it’s not beyond the realm of possibility that Britain’s appeal as a global trading place wanes, hurting the country’s fledgling -if even existent-reputation as a hotpot of cultural diversity at the corporate zenith. Secondly, the Odgers Berndtson analysis also shows that much of the progress when it comes to internationalising the top management has occurred thanks to those FTSE 100 companies not actually based in the UK. Once again, something that’s happening abroad is making the UK appear more international. Only one in 15 CEO roles held at FTSE 100 companies currently headquartered abroad are held by a UK national, in stark contrast to those UK companies based at home. And suddenly it becomes a real prospect that if Britain becomes more insular, Britain’s businesses could become more homogenous-or just British-too. Already now, the number of chief executives of UK origin who head up international companies based outside the UK is negligible. Would Brexit and the inevitable two-year rumble of complicated negotiations and talks really be something that’s likely to change that? And then there we have the occasional comment and headlines which is making it hard for those striving for boardroom diversity not to feel like they’re swimming against a particularly stubborn tide of resentment. I’m thinking of John Allan, the Tesco chairman who last week said that white men are becoming an “endangered species” in top business jobs despite being one of nine white men sitting on the retailer’s 12-person executive board. As a John himself, you’d hope that he’d be acutely aware of the fact that men with his name still outnumber female FTSE 100 CEOs. Finally, let’s go back to the original numbers, dig a little deeper and then remind ourselves that having a sizeable contingent of non-UK CEOs does not necessarily mean that the FTSE 100 is even on the right track to becoming a picture of diversity. Although 40 per cent of the CEOs were non-UK nationals in 2016, an uncomfortable 81 per cent were European. Last November’s Parker Review, showed that of the 1,087 director positions on FTSE 100 companies, only eight per cent were held by people of colour, which is almost half the 14 per cent of the general UK population. A frankly embarrassing 53 companies in the index at the time did not have any directors of colour at all. In fact, just seven companies of the 100 accounted for over 40 per cent of the directors of colour. And of those seven, five have headquarters that are historically located outside of the UK. The crowning data point? As of the end of last year, only nine people of colour held the position of chairman or CEO of a FTSE 100 company. So yes, progress seems undeniable when we look at some of the raw facts. But there’s a strong case that cautious, whispered encouragement may be more appropriate for the time being, than full-blown riotous celebration.