That's what my lab report says, which was Sussex Pathology ltd (which does the testing for onedaytests.com). I can't find much else though.
Here is another testing company, they claim it's based on US ADA recommendations:
Understand what HbA1c is and why there’s more to the HbA1c normal range than meets the eye.
I note that ADA were saying 39 back in 2016:
Pre-diabetes, which is typically defined as blood glucose concentrations higher than normal but lower than the diabetes threshold, is a high-risk state for diabetes and cardiovascular disease development. As such, it represents three groups of ...
But I don't know what changed on 11 Sept in the UK. Are we aligning with the US, or is it just two testing companies with an opinion?