Hi.Take a look at the notes starting here.As the UK is in the EU, HMRC has agreements with other EU countries tax authorities to assist one another in recovering tax owed by a national of one EU country who lives in another EU country. If you look at the third page by clicking on "Next Page" at the bottom right you will see that the UK does have tax recovery agreements with other countries outside the EU but Japan appears not to be one of them. What that means is that HMRC would not get involved in tax recovery action pursued by the Japanese tax authorities but that doesn't mean that they (the Japanese tax authorities) would not try to pursue it themselves through the UK courts. Any such action would have no impact on your UK tax postion.I hope this helps but let me know if you have any further questions.
Thank you - that is useful. I have a few other questions, however. I continued reading the pages that you sent and further along it states "Another country may seek assistance in recovering a tax or duty debt where the debtor lives in the UK. In such cases, treat it as if it were a UK income tax debt for recovery purposes."
But, under the section below that "Grounds for refusing a request for recovery"
It also states that "if it appears to you that the debt relates to a tax or duty that is either not covered by the relevant arrangement or has been imposed by the other country contrary to the generally accepted taxation principles."
In this case, would it mean that Japan is "not covered by the relevant arrangement"?