The Curator
State old age pensions are paid without tax being deducted and it is your responsibility if you have other income that takes you above the personal tax free allowance to inform HMRC so that they can adjust your tax code. Even more important if it puts you in the 40% bracket.The pensions agency were not at fault as you mention.
Ignorance is not always bliss.
I know of someone in my old company who had his state pension paid for many years without being taxed at the 40% and had a nasty shock tax demand for several thousand£ when tax man discovered his code had not been changed to reflect his new additional income where tax was not deducted at source as is the case with the state old age pension including serps