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** I know you will mention claiming the VAT back as we have had this conversation before, but according to my accountant and further consultation with HMRC, because the item that you are selling (BTC) does not atrract VAT, you cannot claim the VAT back for the process of making them. You can claim the VAT back on buying the machines as you charge it when you sell them.
Bitcoin miners are (home) heaters, the hiting by-product are related bonus points - also known as BTC. The manufacturers sells for them (or for many) new and more powerful heaters aka bitcoin miners.
So explain mining protsess to your tax official.