But in our U.K. case this is not so: as others have detailed, the UK-Thailand has almost no information concerning personal income such as pensions (of which there are a large number of distinct types in the U.K.).
No it is not! It is paid from general taxation. The relationship to your NI contributions is only in the decision on whether you are paid a state pension and how much (but the latter is affected by many other factors too).
At present the UK DWP pension is not taxed in the UK.
Mine is! (as I have large SERPS extras).
Just not “at source”:
the tax (a lot!) is collected by deductions (paye) on other income sources.
There is indeed a “similar document” for the U.K. but its contents are markedly different.
Please do not confuse this issue by posting such facts that are totally unrelated to the facts for U.K. taxpayers.