Standards don't set a ceiling on quality, but rather a floor. If we want to sell into the EU market then we will have to meet EU standards.
There was nothing stopping us from setting higher standards for UK producers as those products would, by default, have met EU standards.
The only logical reason for the UK to have our own standards regime is because we want to allow inferior products into our market.
They are a floor on new products. Previous compliance is valid unless or until a new regulation explicitly invalidates a previous standard. This rarely happens in the EU, because in engineering for example, the hard work of identifying safety or other core issues was already done by institutions like British Standards.
The EU are not some all knowing all seeing entity and the rest of the world are just slapdash irresponsible customer killing morons. If a serious safety issue arises, such as an industry standard lubricant suddenly being found to be cancer causing, it's not even remotely true that the EU would be the only place that updates their standards. It infuriates British industry that the British public have been drip fed this idea by a technically illiterate media and Europhile political opposition that the UK are some kind of second rate developing nation, or aspires to be. We are world leaders in things like cancer research.
It is only really environmental standards where they are using a ratchet. In that case, an EU customer that can no longer buy our machines because they're too loud for example, has far bigger problems on their plate than us deciding we really can't be bothered with the EU market anymore (our machines are already quiet enough that you don't need ear protection, because we are actually good at what we do).
British Standards never made a potentially massive regulatory decision that wipes out entire product lines without good reason. The EU found it pretty easy to emulate the bureaucracy and ancillary activity side of standard setting. It speaks well to their basic purpose, adding complexity for its own sake, or to deter non-EU exporters who might threaten EU sectors.
The EU never really got a handle on the fact these things have an impact on their own business's health, because the EU is so large and remote from ordinary citizenry and economic actors that by the time they are even aware a decision of theirs has completely altered their balance of trade, it has already happened.
The EU behemoth had absolutely no clue until it was far too late that German car makers had become entirely dependent on a technology that EU standards were specifically designed over decades to render obsolete. How on Earth does that happen in a well functioning trade block whose standards exist in large part to keep thier own companies competitive?
Their car makers were so busy trying to cater for EU market at a macro scale, fat and content in their free movement paradise, they forgot entirely that the EU doesn't really have the means or the intent to drive innovation as a global power. It is frankly irrelevant to a walled garden with a captured market.
Non-EU car makers didn't innovate because they saw the growth potential in the EU. It's just a happy accident that the follies of the EU mean they are now an additional market opportunity among their global ambitions. And of course, as the EU is prone to do, since it didn't benefit EU companies, this was a market opportunity that was greatly limited when the Eurocrats responded to a looming trade deficit with a planet destroying domestic company protecting policy fudge.
The issue is not size, since US regulators are in close contact with their citizenry and economy. It is bureaucracy. It is mindset. On a good day, the US recognises that making their rules in a vacuum with an intent toward isolationist policy, is a retrograde step. The EU never has these good days. Not even on their radar. They genuinely thought they had created a super power, without ever testing that hypothesis. It's being tested now, and the reality is clear. Left behind.
The edge cases are where the money gets made and competitive advantage tells. Mars has no choice but to alter the recipe of Skittles if one major market decided unilaterally that there is a risk factor. Or far worse, Mars are big enough that if they want to make Skittles "safe" only in the EU, they can.
Mars are not, with the best will in the world, remotely responsible for the majority of UK GDP. Companies like us are the future of the UK economy, at least the part that aims to make anything that cannot easily be emulated elsewhere because it can only done with skills and experience that were hard won over generations through global competition.
As a consequence, we have the luxury of ignoring markets that are relatively small and lack growth potential, which is the EU for the foreseeable future. We have the commercial flexibility to decide if a specific part of our shop floor is occupied for the next six months with building and testing a machine destined for the EU or non-EU markets. It is an increasingly easy decision.
There is indeed nothing logical about ripping up standards to allow global competition undercut our business with products the EU would actually deem to be unsafe. Hence why that is not remotely what this new ability to diverge is about at all. It's about cutting red tape and removing barriers to competition on matters of skill and experience and the actual quality of the product and after market service.