When it comes to the State pension, the tax return demands the amount which the taxpayer is "entitled to receive in the year". That is a very simple figure to calculate.
On the assumption that you are being paid the right amounts at the right times, what you are "entitled to receive in the year" is what you actually receive in the year. That being so, the amount to be entered on your tax return is the sum of the payments shown on your bank statements within the tax year, i.e. at any time from and including 6 April to and including the following 5 April.
That is what the DWP should be calculating.
Unfortunately, however, the DWP is not providing HMRC with the information on which State pensioners' tax liabilities should be calculated. Both almost certainly know that there is a massive problem insofar as State pension data being passed from one to the other is concerned.
HMRC Admin 11's reply to you is an example of how HMRC try to fob State pensioners off. When I, acting on HMRC's advice, spoke to someone in the DWP about this matter, I was very clear that I needed what the tax return demands, i.e. the amount I am "entitled to receive in the year". They sidestepped my request completely - a two-page letter, there was plenty of waffle but the figure sought by me was mentioned nowhere.
I have now written to my MP.