Even if a pharmacist could check your blood sugar, it'd only be a one off result of your blood sugar at that time and, if it indicted a possible issue, then you'd have to go back to your GP anyway.
They can do a very clever blood test which gives, as I understand it, an average blood sugar reading over a three month period, so more info than a one off test of your blood sugar at one particular time.
I've had a few higher readings before now on a general blood sugar test but the longer test has been very helpful in checking my blood sugar generally and determining that it's not diabetes.