There is one good reason for Japan wanting to do this: it has come to the apparent conclusion that Bitcoin is a commodity used for speculative purposes and not primarily as a currency just as the UK has come to the reverse (incorrect, I think) conclusion.
Japan also wants to impose a tax after the collapse of two Bitcoin exchanges within days of each other leading to the loss of significant numbers of the supposedly always traceable currency, giving a lie to its supposed transparent quality for crime-beating purposes and to its merit as a regulation free zone. Tax, it is thought by Japan, would help impose that regulation.
It looks like HMRC made the wrong decision at the wrong time. There’s always time to reverse it.
Here’s someone explaining what the UK and Japanese approaches to the taxation of Bitcoin are.
The use of Bitcoins in a transaction is treated just as any other method of payment for goods and services. If VAT or sales tax on the goods and services is due then it will be due whether people pay in Yen, Pounds or Bitcoin.
The purchase of Bitcoins themselves will not be subject to VAT or sales tax as purchases of Yen, Pounds or other variations of currency are not.
The mining or earning of Bitcoins is subject to exactly the same taxation as any other method of trying to accumulate pelf. Income minus costs equals profits that are then taxed at the appropriate rate for the vehicle which is used to do said earning. A sole trader is taxed as a sole trader, a corporation as a corporation.
The only interesting thing at all will be whether mining rigs, which tend to deteriorate in value from large to spit in about 3 months will be able to have some form of accelerated depreciation. Perhaps be written off in the first year.
And that’s it. And do note, the Japanese and UK taxation systems are exactly the fucking same on all of these points.
And how else did anyone think that Bitcoin was going to be taxed?