One of my first jobs was at HMRC in Southend, checking import paperwork to make sure the trader had used the correct customs classification - and paid the correct duty. There were hundreds of us, dealing with the volume of paperwork before the Single Market.
When the SM came in, we were let go and some went as far as the Russian ex-republics to show them how to collect customs duties and VAT (using an AK47 usually)
To give some hope to @Whisper and other bike companies, the level of customs error then was low as companies get used to new ways of working. The paperwork may seem a pain but computers systems now are quite capable of handling the complexity cheaper and quicker as long as you avoid the PICNIC problem (Problem In Chair and not in Computer)
If you were to accept advice, though it hasn't been asked, find someone that knows the current system and pay what they ask until you get used to the new ways. Now where did I put that AK?
Good luck.