So, you have (at least) the following principles:

Business-to-business (B2B) sale and both seller and buyer have VAT number of the Member State in which they are established: the place of taxation is determined by where the intra-Community acquisition of goods is made (i.e. the Member State where the goods are finally located after transportation from another Member State).

Businesses selling to non-taxable legal person, small enterprise, VAT exempt entity: normally, VAT of the Member State of origin of the goods, unless a threshold per customer has been reached: then it's VAT of the Member State of final destination of the goods.

Businesses engaging in long-distance selling to individuals and/or to non-taxable legal persons, small enterprises, VAT exempt entities (i.e. threshold for those transactions has been reached): VAT of the Member State of final destination of the goods.  Not engaged in long-distance selling (i.e. threshold not reached): VAT of the country of the seller.

So, are you sure that KNCminer sells for more than 70,000 GBP into the UK to non-registered customers? Because the threshold has to be checked on a per-country basis and is also different for each country. Actually, I think only they can know for sure.

Conclusion: billing address is not relevant for VAT purposes.