Potential exporters not only have to ensure their goods conform, they must provide evidence of their so doing. This requires putting the goods through a recognised system of what is known as "conformity assessment".
We are at this point entering serious nerd territory. If your eyes are beginning to glaze over, all we can say is welcome to the world as it really is. It has taken years of mind-numbing, tedious study to understand this amount of detail, and either you know it, or you don't.
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But the moment we leave the EU, this stops. Your component manufacturer may still comply with exactly the same standards, but if the product requires independent testing , any testing houses and the regulatory agencies are no longer recognised. The consignment has no valid paperwork. And, without it, it must be subject to border checks, visual inspection and physical testing.
What that means in practice is that the customs inspector detains your shipment and takes samples to send to an approved testing house (one for the inspector, one for the office pool, one for the stevedores and one for the lab is often the case). Your container inspection is typically about £700 and detention costs about £80 a day for the ten days or so it will take to get your results back. Add the testing fee and you’re paying an extra £2,000 to deliver a container into the EU.