Thanks for the response Alison,
I've read this about blurred vision and haven't experienced this atm - although of course this could change. I guess asking anyone for advice on this is going to be problematic at best anyway - as people could feel responsible for what I may do if they give advice.
I think, as I believe my eyesight is not too bad with my glasses (at least long distance - my close up vision isn't great but I don't need to be able to read food can labels while driving!), I will send it off saying my eyesight is good enough. If after a new prescription they say it isn't good enough even with new prescription then I will inform them of a change. It does say "if you are unsure get advice from your optician" but it doesn't say "don't drive until you have that".
Your point about changes in my vision over the next few months is a good one. I have already pointed out to them when I made the appointment that I had just been diagnosed (the day before) with type 2. Problem is, I haven't had my eyes tested for 4 years+ and I know they are worse than they were back then so I don't really want to leave it months to have them tested again. I will speak to them though when I see them. If it means that my prescription will end up being a temporary one (or likely so) I will just make sure to get some cheap glasses until I know its more permanent I guess.