So, after a great many emails and numerous false starts (don't damage your wheels in high summer if you can help it...) a set of wheels has finally been ordered and I hope will be delivered within 10 days - so I'll be back on the road during August I hope.
In case of use to anyone else, the dimensions of my original Aero 8 s4 wheels (which proved a matter of some debate) are:
18 inch diameter
8.5J front and rear (width)
PCD 114 (wheel nut spacing)
ET 30 (offset).
I've had great assistance from (among others) Sarah at Brands Hatch Morgan, Gary at rimstyle.com and Damian at wheelbasealloys.com.
When the new wheels finally arrive and are fitted I'll let you know what I've bought and from where and will post a photo.
Thanks to everyone for their advice on the forum.
Beard