what you need is the car pass available from main stealers approx £25-£50 depending where you go, this will give you radio code plus you will need v5 and other id passport, driving licence,
the only trouble with this is it will only give you the cars original radio code so if radio has been changed or recoded the code will be wrong, another way is contact davednd on the forum who can usually supply you a code for the radio you have 

Which stereo do you have?

Have a look at my website below - may help