You state that your GP is referring you. So I take it that you are in the UK. If so, please insist on going to a clinic that is managed by Moorfield - I won't let anyone but them touch my eyes. What may be recommended is that they may need to do some light retinal laser 'tidying up' of your retina. This will clear your retina from any bleeds or leaks or cotton wool spots, that may be affecting your vision. So then, with a clear retina, and tight glucose control, you should achieve better vision straight away. If, however, your eyesight is not that good due to cataract formation, you will need to have this removed to improve your vision, although Moorfields prefer that you wear corrective lenses on your glasses before they recommend surgery.to remove a cataract.
In general, once your glucose control is optimised, your vision should improve. The diabetic eye is the only one that can change shape due to high glucose content (it's like osmosis, if you remember it from school). So imagine an unpeeled potato versus one that has soaked in water for a while. You won't have the same vision from them, and likewise this is the state with your eyes. For now, try blowing up everything on your computer, so that you can get by. It won't be long until you can see again - and GP referrals should go through to both the diabetes and eye clinics for them to cross-reference your notes and get you seen in a timely manner.
Best wishes!