There's no import duty from EUR to UK and no VAT due at the border either, under the postponed accounting scheme. Should pass through unimpeded.
Are you sure about that? According to this page from UK government, for goods worth more than £135 in total, you will have to pay VAT + Customs Duty.
Did the seller (siglent.eu) already charge you the VAT? If not, I suppose you have to pay it to the courier, and the courier is supposed to transfer it to the UK tax office. Same for the import duties. And the courier will charge additional administration costs.
Hi. Yes I am sure about the VAT. It's called the postponed accounting scheme, and as long as my VAT number is displayed on the invoice, VAT is not charged. Same as before. This is because it's a business purchase and I am VAT registered. The 'rules' changed I think in July 2021. It's all very confusing, but yes, for VAT, if it's a business purchase, the VAT is just not charged, rather than being charged and reclaimed on a VAT return. So it now works just like it did before with EU imports. I read online that I should get an EORI number, so I did do that, but so far nobody has asked for it or displayed it, and I buy Mikrotik networking gear from Latvia without issue. The EORI number I was issued by the UK gov is actually identical to my VAT number, just with a 3 zeros at the end
However, upon further reading (can't get through to UPS on the phone), I suspect I have fallen foul of the 'origination of goods' issue. The no-duty thing, or 'preferential tariff' from the free trade agreement only applies if the goods actually originate from the other country. I guess the Siglent stuff originates from China. This is why all the Mikrotik gear I order from Latvia comes through without duty and without VAT, but this 'scope and test board have attracted 20% duty (no VAT). Oh well you live and learn! I suspect I'll not get a swift reply from UPS so I'll just pay it and get playing with my new toy.
It does make me wonder what would happen if I ordered some Ubiquiti stuff along with Mikrotik from the same supplier in Latvia. Ubiquiti being USA originated.