My current wheels came with 205 width AD08s on the front, which are very good, and 225 width crap tyres on the back. So the rears need replacing with a pair of AD08s to match the fronts. However, in 15" these are only available in 185, 195 or 205 width. I could move the fronts onto the back and get some narrower fronts, since narrower front tyres seem to be the usual arrangement.

So my options are 185/205, 195/205 or 205/205. Thoughts? Car is a 7 with 735 kg/320 bhp.

I'm currently leaning towards 195 front 205 rear as a compromise.

What width are the wheels? They might be too wide for a 185 or 195 tyre

6.5 on the front, 7 on the back. So I don't think that's an issue, the fronts should accomodate 185 and the rears should be fine at 205.

I would get the existing 205s put onto the 7" rims for the back and then a pair of 185s on the front 6 1/2" rims. The general thinking when it comes to cars as light as ours as money is best spent on better tyres rather than wider tyres.
Wide tyres on the front just spread a light load over an even bigger surface area and reportedly can increase bump steer and tramlining. I know someone who went from 205s on the front down to 175s and found the car a lot more pleasant to drive.

Update: just did a day at Bedford with 15", 185 front 205 rear (AD08s, 205 is as wide as they go in 15", as notanumber suggested. Feel and balance was very good, really couldn't fault this, but overall grip (and hence cornering speed) was lacking compared to a friend's atom (on 225 width R888s).

Grip seemed to significantly improve the more I lowered tyre pressure - at the end I was running 19 psi hot down from a starting point of 24, maybe I could have gone lower?

Not keen to replace all four tyres with some wider R888s (would have to replace all four as Yokohama sadly don't make a 225x15" AD08), but do I have any other options...? Was thinking 205/225 to keep the balance the same?

Any thoughts?

I've gone down as low as 14psi hot on a similar weight car, however, that was with race tyres with stiffer sidewalls/beads to keep them on the rim.