Tax free savings affecting wife's tax code. Why?

Descrabled

Ms Descrabled had exactly the same problem for many years before she reached state pension age.  Many unhelpful HMRC phone reps tried to explain away this problem that arises from their computer program.  Eventually we talked to a helpful Lady from HMRC who gave us the solution.

Inform HMRC that her non savings earnings are going to be somewhat higher than they presently believe.  We used to add £1.5k to her expected private pension income each year during July-August and informed HMRC that was to be the total pension for that year.

One year HMRC wouldn't accept this imaginary increase and she ended the year paying £2 too much tax.  Complaint made no difference until our MP worked his magic wand.and HMRC sent her the £2 overpayment and £25 compensation.

Ms Descrabled has never had problems with HMRC since that time.