Many thanks for your reply - most helpful.
The income is indeed from s/e and above the threshold. The tax returns for all years 2016/17 onwards included the relevant Cl. 2 entries as they were properly completed by her agent. I don't know why your colleague suggested she pay at the 2021/22 rate for the 4 years concerned (2106/17 to 2019/20 - 2020/21 return has been amended) but as she needs to call your colleagues again she can ask that question. At the end of the day the difference is only about £20, so she may decide it is not worth arguing...
I will speak with my friend again as I am 99% certain that she was not given payment instructions and she did not mention a letter - it was me who suggested to her that it may take a while for HMRC to contact her regarding those earlier years given that she had not received payment instructions. Anyway, she may simply have mis-heard or misunderstood next steps as she was struggling enough to ask the relevant questions in any event!
I will ensure she calls again to obtain payment instructions and to clarify/finalise the amount due for those 4 years but unfortunately, being with her during the call is not possible as we live 300 miles apart and I am not sure she can ask you guys to "phone her friend".
While talking with a friend about her NI record and state pension forecast we discovered that despite submitting Self Assessment returns for many years in relation to her self-employment, something caused HMRC to ignore her self-employed status from 2016 onwards and to adjust the amounts shown on her self-assessment return such that no Class 2 was actually collected. She did not notice this small reduction in the amounts payable and as a result her NI record shows empty years for 2016/17 onwards. She understands none of this and her tax accountant is being summarily unhelpful.
Having read various posts on this forum and done a lot of internet research I tracked the issue down to the changes in 2015 when HMRC started collecting Class 2 NIC via the tax return and suggested she call HMRC's NI team to correct the issue as something clearly went wrong at that time.
She did that and the team have corrected your systems. For 2020/21 the Class 2 is now showing as due by 31 January 2022 and she was told she would have to pay the missing NI for 2016/17 to 2019/20 at the current rate. She is happy with that, though personally, I think there is an argument that it should be the rate for the year in question but let's leave that to one side.
What is not clear is how she actually pays the £635 or so. It is a couple of months since she called HMRC and she has received neither a letter, nor any payable amounts (other than the 2020/21 mentioned above) added to her SA account. Will HMRC write to her at some point providing a payment reference or other instructions on how to pay, or must she do something proactively still to create the payable amounts?
As I said, she understands none of this, her adviser is "not interested" in contacting HMRC about it and if she calls HMRC again she will likely not fully understand what they tell her (she is particularly "overloaded" at the moment having recently lost her husband meaning she is dealing with a myriad of complex issues as a result), so other than sending a 64-8 adding me as her "agent" (something I do not want her to do) we are not sure how to enable her to pay the amounts accepts she has to pay and which are needed to secure her state pension next year.
Belgian tax is not my area of expertise but a quick read of the Belgian Finance Ministry pages would suggest that non-residents (broadly the people this thread is talking about) only qualify for the Belgian personal allowance of currently 8,990€ if their "earned income that is taxable in Belgium amounts to at least 75% of the total earned income (both the Belgian and foreign earned income)". I have not gone further to see if there are age-related allowances as well.
The site also states that while worldwide income needs to be entered in the appropriate boxes on the non-resident tax return, it is neither taxed, nor does it feature in setting the tax rate for the income that is taxable in Belgium.
I would suggest that those with Belgian pensions may want to do a little more research to establish what tax they will have to pay...
As I said previously, I am following this discussion purely out of interest. It is encouraging to see that the position is finally becoming clearer, albeit with the outcome I feared in my post from 4 months ago. Despite that, I am sure those affected will welcome the certainty now being provided.
The note above sets out the normal 4-year rule for making repayment claims but makes no mention of the possibility to make a Mutual Agreement Procedure (MAP) claim to obtain repayment of the 2 years preceding that, i.e. back to 2016/16. I don't know the extent to which anyone affected would need look back that far but it would be helpful if HMRC could set out the position regarding MAP claims in relation to this issue.
I believe you need to make an overpayment relief claim for the previous 4 years and then make a Mutual Agreement Procedure (MAP) claim to obtain repayment of the 2 year preceding that. Given that the UK had no taxing right over the pension, it is a good question whether you can obtain repayment for any earlier years but I think the normal rules would get you back to 2015/16 tax year.
I am following this thread from a general interest perspective and fear Belgium is probably correct in its interpretation, as indicated in the above letter from HMRC.
My reading of the Convention is that Article 18(a) gives taxing rights to the paying country unless overridden for pre-2013 pensions by 18(b). That paragraph requires the pension to have been paid under a "pension scheme", a term defined in Article 3(1)(l). My reading of that paragraph is that state pensions are not within its definition of "pension scheme". Indeed, Article 3(l)(ii)(A) appears not to include state pension arrangements and (B) specifically excludes social security schemes.
Perhaps HMRC could run that past their specialists and give a response from them.
We bought a couple of years in 2019 and it took a few months to appear on the record.
In most circumstances it really doesn't matter how long it takes to appear as it is about paying NI to fill an identified year in the NI record. If this is not being done immediately before claiming the pension then knowing it has been correctly added to the record provides only peace of mind; if it is immediately before claiming, then the pension paperwork showing the actual level of pension and so on will either be correct or not, in which case clarification can be sought...
I would not worry and just check back from time-to-time as I really cannot imagine that it will not be correctly added...