Actually, UK law does not currently allow you to rip music (or any other media - see below for one exception) without the copyright holder's permission. It has been recognised that this is somewhat outdated given the prevalence of MP3 and other media players, but AFAIK no changes to the law have been made as yet.
In the US, there is a "fair use" clause that does allow for making backups and using on your own MP3 player etc but not in the UK. (Apart from some obscure allowance for software that dates back to the days of floppy disks and tape drives).
That said, I can't see anyone bringing a prosecution as long as it was genuinely for your own use - mainly because of the resultant bad publicity.