Crypto networks are not run by any specific government or group of individuals, compared to other securities like US shares.
So what is the geographical status-quo of cryptocurrency for UK tax purposes?
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This is certainly a complicated topic and it's highly likely that the future will bring us major modification to the official guidance, but as of 2019-2020, the answer is no. Capital gains realised by selling cryptocurrency are NOT foreign income if you're a UK tax resident when you buy and dispose of them.
HMRC considers that throughout the time an individual is UK resident, the exchange tokens they hold as beneficial owner will be located in the UK.
HMRC has considered other possibilities, but at this stage in the development of these tokens has found that a residence basis most accurately fits the majority of transactions.
This means a person who holds exchanges tokens is liable to pay UK tax if they are a UK resident and carry out a transaction with their tokens which is subject to UK tax.
Using the residency of the beneficial owner of the exchange tokens to determine the location gives a clear, logical, predictable and objective rule which can be easily applied.
Of course, this gets really, really murky if you're a tax resident of the UK but domiciled somewhere else (and potentially a dual resident), because your home country might have a different opinion about the location of cryptoassets, so in this case consider talking to a professional tax adviser if you hold big bags of cryptocurrency.