Here's my take on it:
The thing you have to understand is that NHS guidelines have been around a while, are selected by a committee, and economic factors play a part (let's face it, the lower the diagnosis threshold and guidelines, the more it would cost the NHS to support, educate and train all those diabetics). There is also a widespread expectation within the NHS that diabetes is progressive, leading to increased medication and complications that develop over time.
In contrast Jenny Ruhl, on the 101 website, constantly re-evaluates new research and uses that evidence to suggest blood glucose levels intended to minimise the chance of ever developing diabetic complications.
I choose to aim at the 101 suggested BG levels.
Of course, you should make up your own minds.