I used ESC A19 successfully for a friend who'd received a demand for £2500 uncollected PAYE back tax relating to two recent years. They allowed the earlier year and refused the more recent year because it was too soon for ESC A19 to operate. I was able to inform HMRC that the Treasury Minister had recently issued an instruction to HMRC, that where their failure to collect PAYE back tax related to the State OAP, under no circumstances were they to attempt to do so. There was no further argument. It did not matter that there was no actual apology because I discovered that the failure to collect had been going on for several previous years, though they were issuing plausible tax codes and patronising reassurance each year.
Regrettably this sort of thing is commonplace. The LITRG website provides a wealth of otherwise little known detail, not only for unrepresented low income folk, but for anyone with PAYE problems with HMRC, which enabled me to win that one. It is a philanthropic arm of the Chartered Institute of Taxation.
There is a legal precedent from a few years back which basically says that if one UK Government Department has been given the information, ALL Govt Depts are deemed to be aware of it. I imagine it should equally apply to different branches of the SAME Dept – ie HMRC. I could probably find a reference if anyone wanted.
All the above should apply equally to any UK based PAYE customer of HMRC, whether military or civvy. I have no knowledge of ex-pat stuff though.
I would add that a Tax Code is only a tax officer's best guess for the current/next year. Whether the error is large (requires dealing with now) or small (could be postponed) the true position will usually only emerge after the end of the tax year. Anyone with any doubts would be well advised to do their own calculations for verification, though some ex-colleagues of mine (civvies) who are PAYE and are not required to submit tax returns, and who should know better, still leave it to HMRC to do the annual reconciliation, and then wail ** when faced with unexpected demands when they really have no idea if the demand is correct or not. An acquaintance recently received a surprise demand for several grand .... and paid it.
** BTW I am not referring to anyone posting here about AFPS of which I have no knowledge. In any case, if reasonable self verification had been carried out, there should be no problem unless HMRC had made an error - perhaps later - or had invented raw data - as happened in a couple of my strictly amateur cases.
LFH