So much of the initial work on a return by a tax authority is put on computer these days, with little 'human' interaction.
The folks at HMRC, although not the instant knowledgeable people of days gone by, are still pretty good at finding a solution to a question. You may have to ask to speak to a supervisor, but a call to HMRC may establish 1) reporting requirements for your situation, 2) if needed, how and where to report on the SA form, and if needed, 3) what to write in box 19 (page TR 7).
A call to the HMRC help line will now get you the voice interactive answering function, so key words may be 'international income' or 'pension'.