The odd thing about today’s decision to allow Huawei to help build the UK’s 5G network – albeit with the company’s overall involvement capped at 35% of the market – is that the real decision was made years ago.

Because Huawei has already helped to build the UK’s 5G network, which is running in cities across the nation. You don’t have to take my word for it. If you know what you’re looking for, you can spot Huawei towers on rooftops and cabinets on street corners. If you really know what you’re looking for, you can even tell which of them are beaming out 5G signals. And even if you can’t, there’s always the chance that a messy contractor has helpfully left the packaging lying around with the Huawei logos clearly visible.

If you’re wondering why the conversation about blocking Huawei from the UK’s networks has had an air of quiet desperation to it, there’s your answer. For all the outspoken opposition from the Atlanticist wing of the Conservative party, no one ever came up with a good answer as to how, practically, Huawei could or should be banned from providing equipment that it had already provided, to mobile networks who desperately wanted to keep it there.

‘We’ve never ‘trusted’ Huawei' Ian Levy, technical director of the UK’s national cybersecurity centre

That isn’t to say it would have been impossible. It just means that, at a rough estimate, it would have taken a meaningful fraction of the cost of an HS2 – in the tens of billions of pounds – and another two or three years of implementation to strip out Huawei, replace it with equipment from Ericsson or Nokia, and slowly crawl back to exactly the same level of coverage we have today. That would have been the carriers’ money, rather than the government’s, but it would almost certainly come out of the pockets of Britain’s consumers one way or another.

Even that expense wouldn’t account for the losses chalked up to Britain falling from 5G world-leader to 5G laggard. It’s easy to roll your eyes at telecoms executives breathlessly talking about the fourth industrial revolution and the role new cellular standards have to play in enabling that transformation but there is a real economic benefit to having better connectivity, and a corresponding cost to lagging behind.

None of which is to say that Huawei should be trusted. And, indeed, it isn’t. “We’ve never ‘trusted’ Huawei,” said Ian Levy, the technical director of the UK’s national cybersecurity centre. You can see that lack of trust in the fact that, uniquely, the government set up the “Huawei Cyber Security Evaluation Centre” – HCSEC, a world-first operation that sees the UK state directly assessing Huawei’s capability. That exists, Levy says, “because we treat them differently to other vendors.” In fact, the nicest thing that the HCSEC has to say about the company is that its computer code is so tangled, and its operating procedures so arcane, that it’s borderline impossible to truly tell if it is is safe or not.

The National Cyber Security Centre’s analysis for the sector at large, meanwhile, is dryly blunt. The most-discussed fear of Huawei’s involvement – that the company could be used to give the Chinese state privileged access to Britain’s network – is dismissed in a rather unreassuring way: “Placing ‘backdoors’ in any Huawei equipment supplied into the UK is not the lowest risk, easiest to perform or most effective means for the Chinese state to perform a major cyber attack on UK telecoms networks today,” the analysis notes.

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The true fear isn’t really technical at all: it’s economic. It starts from a perception – not altogether unfair – that the company grew so massive by leveraging state aid that would be illegal in Europe, selling equipment to markets in Asia and Africa that were paying for it with low-cost loans from the Chinese state, and receiving immense direct government support for research and development. Now, according to Franco Zaro of cybersecurity firm Valid: “Huawei has had a more global presence than Ericsson and Nokia combined.” It may be genuinely better and cheaper, in other words, but only because it didn’t play fair to get there.

And however it got where it is today, there’s a corresponding fear about where it will go if it continues unchecked. It would already be hard to remove the company from 5G networks; but what if it grows so dominant that in a decade it’s impossible to even build a 6G network without Huawei’s, and thus China’s, involvement?

Hence a 35% cap, designed to ensure that other companies retain the capability and scale to compete with Huawei on its own turf. And hence, really, the answer to the question: why now? Because for most of the past 20 years, the west has been more than happy to let China build things cheaply and to reap the ensuing savings. Now that the downsides are becoming apparent – and now that the US thinks trade wars are good and easy to win – it’s embarrassing to have to admit that the tradeoff might not have been worth it. But that doesn’t change the fact that the trade-off has already been made.

• Alex Hern is the UK technology editor for the Guardian