Blood tests

A normal blood test only shows the BG level at the time the sample was taken. A HbA1c test shows the average BG over the previous 3 months.

At one time to confirm if somebody was diabetic it was common practice to take two consecutive fasting blood/glucose reading a few days apart and if the results were at/or exceeded 7.0 mmol/L the the individual was considered as diabetic.
These days may doctors follow the WHO guidelines and diagnose if someone is diabetic or not directly from a single HbA1c blood test, though some may back this up by requesting a fasting blood/glucose test as well.
These tests will obviously not be applicable to someone who's blood/glucose levels are such that they have had to be admitted into hospital with perhaps a coma, or obvious diabetic symptoms as would be the case of Type 1 diabetes suddenly developing or with some underlying other medical complication.

I'm slightly surprised that your annual test didn't include an HBa1C as I think it should have done to follow NICE guidelines assuming your are diagnosed as diabetic which as you say you aren't quite yet. Fasting blood tests to be honest aren't of much use other than to indicate if you are quite seriously diabetic. The HBa1C measures the weighted average blood sugar over the last 3 months and is a very good test for diabetes. A fasting test can be influenced by liver dumps of glucose in the morning so can confuse the result. It is also a 'spot test' whereas the Hba1c is along-term average.