advice

I would say that your blood sugars are either too high or too low and as you do not test, (as seen in your previous posts) then it is difficult for anyone to know what is going on. I cannot understand why the surgery is happy to supply a meter and lancets but not test strips. What does your Dr. consider to be normal levels and is this because of an HBA1c test?

Can you enlighten us as to what you consider sensible meals and snacks.

If you are employed here in the UK there are legal requirements that your employer must abide with in relation to your work. Having diabetes is considered a disability and as such your employer should be made aware of it, and ensure that you are catered for.
The legal requirement list the working temperatures (hot as well as cold, ventilation, lighting, sound levels) as well as many other things. Having diabetes should mean that you are entitled to more frequent breaks, where you can eat/drink. If you have union representation then I'm sure that they can help in this respect.
It might also be worth while trying to source test strips maybe over the internet so that you can at least see if your B/G levels are being effected. Also remember that in a warm/hot environment you will need to replace any lost fluids and prevent de-hydration on a regular basis.
I'm on Metformin myself and haven't experienced all the problems that you mention unless it's a particularly hot day and I get de-hydrated and have walked some distance.