Use this.
fillable Nominet form
You only have to type in your details once and then either a) save the pdf to your hard drive with your details inside or b) print off several copies with only the domain name to fill in.
Press submit to get your details frozen into the Nominet form. Save on your hard drive.
Uses adobe reader. No 3rd party downloads needed.
Try it out with a few letters if you like, you can change it again (as long as you press submit button.)
yesterday.