For anyone joining the British Foreign Office in 1998, as I did, and having an interest in China as part of their life before they became a diplomat, working alongside veterans of the almost two decade negotiations over the handover of Hong Kong, which had happened the previous year, in 1997, was hard to avoid. The main sections dealing with China in London, the British Consulate General in Hong Kong, and most of the posts in the People’s Republic itself, right up to the most senior level, were stuffed with those who had played a part, large or small, in working out the finer detail of the reversion of sovereignty to China.

That the process had gone relatively smoothly, despite significant hiccups during the Patten governorship from 1992 became a source of pride. Colleagues talked about those choppier moments, and about how hard the going was sometimes. They referred to the trauma of the 1989 uprising and the panic that had given rise to locally. But by 1998, it was not rare to hear British government officials and their political masters talk in the same way as their Chinese opposite numbers, of the handover of Hong Kong being a “success”.

The management of the Hong Kong issue came to be held as evidence of British negotiation effectiveness. Around the middle of the next decade, when doing some work on East Timor – previously a Portuguese colony till Indonesia assumed ownership over it, and then its independence in 1998 – I was talking to someone who had worked on the Hong Kong issue through the 1980s into the 1990s. “We did a good job with cleaning up our colonial issues,” they bragged. “Look at the mess Portugal made everywhere, just clearing off and leaving others to clean up the mess.”

Historians might dispute that assessment. But it typified a mindset where the onus was on an almost paternalistic sense of responsibility, and of Britain’s awareness of its duties and knowing how to fulfil its responsibilities. It also exposed a bureaucratic and political commitment to sticking rigorously to international agreements and rules, and abiding by them.

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Whatever punctiliousness and scrupulous attention to detail officials and politicians paid to the smooth management of Hong Kong’s reversion to Chinese rule, one thing was clear. It took a solid decade or more from the outline agreement of 1984, the Sino-British Declaration, to the final realisation thirteen years later of intense, complex and sometimes torturous negotiations and preparations. If anyone in 1984 had said this whole process had to happen in two years, the response would have been a frosty one. It would, no doubt, have been regarded as impossible.

Hong Kong’s return to China was a complex matter, but for most British remote. And, for the UK, it pales in insignificance beside the exiting of the EU which the UK is now implementing. In terms of scope, complexity and potential impact on daily life, Brexit occupies another order. And yet, bizarrely, while the UK gave itself plenty of time for a moderately complex issue, on one far more perplexing and torturous it is running like a lemming towards a cliff edge heedless of what might happen once it goes over.

Talk of a no deal outcome has become increasingly common since the first attempt by Prime Minister Theresa May to nail down a Brexit deal in early July. Widespread dissatisfaction with that led to high profile resignations, and immense tussles in parliament. It is likely this is only the beginning of a hugely difficult process that now shows every sign it could end nowhere. There is even talk of a second referendum, something that would be high risk, and extremely unlikely to change the original June 2016 result.

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Hong Kong did not arouse domestic constituencies in Britain – or only on a minor scale, because it was regarded as a foreign affairs issue. Brexit gets input from everyone, because it impacts everyone. The EU, in the UK, has always been the single foreign affairs issue which has traction in domestic space. Even so, it is puzzling that the UK was so punctilious and careful about observing its obligations towards Hongkongers (that at least is what it claimed many times before, and after, 1997) and yet is being so slapdash and unthinking about its obligations to itself.

What can one read into these two very different kinds of behaviour? One explanation is that there is almost a mood of national self-harm coming through in the way the UK is looking after its interests at the moment. With Hong Kong, it at least tied down its financial and economic interests, because it was in these areas that it wanted to see stability no matter what happened post 1997. But even these basic points seem to be up for negotiation with the current iteration of Brexit. There are many Brexit supporters who feel there are identity issues that are more important than prosperity, and preservation of a decent standard of living, even if they often have problems trying to spell these out.

One thing we can learn from Brexit, and comparisons with what was the final major dismantling of the residue of empire in 1997: the British when negotiating over something more remote and removed from them did so with a clarity and patience that even impressed their Chinese interlocutors. That’s why the deal worked. A potentially chaotic situation in July 1997 was avoided. A city went to sleep under one administration and woke up under another with hardly any noticeable changes in their daily lives.

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Brexit, however, involves emotion – and the British have proved poor at handling situations in which there is so much clashing with usual rational frameworks for dealing with events. The urge by some is simply to go for it, leave the EU and let the devil take the hindmost. Over Hong Kong, the UK never adopted such a reckless position, and rightly so. Over its own affairs, it has proved far less charitable. And that says something very profound about the complexity of how it really regards itself and its national position.

Kerry Brown is director of the Lau China Institute, King’s College London