Hello, I'm Keith and happy to help you with your question.
My immediate solution is for you to present your own petition the Court for bankruptcy. If you are made bankrupt then the debt to HMRC and the constant hassle will disappear.
A second solution is to apply for a Creditor's Voluntary Arrangement, but this needs acceptance by your creditors and if HMRC are the only organization to which you owe moneys that consent is, needless to say, unlikely to be forthcoming.
One small point, when you left these shores did you send a form P85 to your tax office? If you did not you should remedy this deficiency. This will make you non resident from the date of your departure.
A personal bankruptcy might have serious implications in the country where you are now living. You will have to take this into account.
You should approach an UK solicitor without delay for guidance on how to proceed.
So sorry to have to rain on your parade, but you require specialist assistance immediately.