Crover - the HMRC declaration relates to sales / purchases / profits on bitcoin or other cryptocurrencies.
It does not relate to purchases of what at the end of the day is electronic hardware. This is no different than if you buy a PC or laptop whether from PC world (where the VAT is included in the price) or from abroad where HMRC require you to pay VAT on delivery.
Many ebay sellers undervalue / pretend they are sending a gift in order to avoid you having to pay VAT / duty on the product. Not only is this illegal, but you as the recipient are liable for any false declaration.
It may well be that due to the large quantity of Antminers being sent to the UK that HMRC have got wise to Bitmain undervaluing and told them to ensure the correct duty is charged or they will seize shipments, which I am afraid they are more than entitled to do.
I'm no fan of paying tax any more than anyone else but I'm afraid there's no easy way round it.