Zaphod,
The biggest difference between the eyesight requirements for driving & for flying is the fact that for flying in the UK your *uncorrected* vision is taken into account.
For a PPL you need a class 2 medical, which means your prescription must be between +5 and -8.
Regarding the "reading of a number plate" for driving, I think the standards are probably about the same for flying; I remember having to read letters on a chart, but not sure if it is exactly the same as driving standard or not. Very similar anyway.
If you wear glasses or contact lenses, then you also need to carry 1 spare pair of glasses with you in the cockpit.
I decided I wanted to learn to fly about 10 years ago (just PPL, not interested in CPL). I phoned the CAA medical people at Gatwick & told them my prescription (very long-sighted; +5.00 in one eye, +5.50 in the other). They told me that my eyesight was outside the accepted range even for PPL, & that there was no way I would ever be allowed to fly - end of story.
However, whilst talking to a flying instructor one day at an air show, I was given the number of a nearby doctor who could do CAA medicals; I went to see him & told him about one of my eyes being worse than +5.00; he simply replied "yeah, but your other eye is within the limit so don't worry about it." He gave me my medical certificate & I've now had nearly 10 years of happy flying! If I had just listened to the CAA person at Gatwick I would never have got my licence.
I've also had LASIK surgery a few months ago. While my eyesight now is more or less perfect, I'm concerned about whether or not I'll be able to renew my medical, as I've just been reading about how the "pre-LASIK prescription" must not be worse than +5.00 (the original doctor I saw has since sadly died, so I need to find another doctor who is flexible on this; I'm sure if I went to Gatwick to get my renewal I would fail).
John