Looks like they're different kits...
http://www.eibach-suspension.co.uk/tsearch.php?search=BMW%20Z4%20Eibach
There's a better Eiback site I was on the other day, if I find it again I'll post - it had the part numbers.
EDIT... here you go...
This is from the international site, suspect the part numbers are the same for UK...
Z4M - 2095.140
2003 model 2.5 / 3.0 - 2073.140
To double check...
http://eibach.com/cgi-bin/htmlos.exe/032.10.3452139347500005800