Unfortunately you need the serial number of the radio in order to unlock it. You must remove the radio from the dash and you will find the serial on a sticker on the case. There is no other way round it as the serial of the car is not relevant with these Ford radios unlike some other manufacturers.
For European Ford radios the serial begins with a letter then 6 numbers e,g M123456.
It is this number you must find in order to have the code processed. The radio can be removed from the dash with special tools which you can obtain from the likes of Halfords for around £5. Halfords staff will usually be happy to assist if you need them to pull the unit out for you.
illustrates the radio removal process for the Ford Focus.
There is no other way to decode the radio. Even Ford themselves need the serial of the radio to retrieve the code but will charge £20 to £35 to provide this.
One alternative is to use this site
which does the codes for £3.50. I have used it a number of times for these Ford radios and they are very reliable and cheap compared to Ford.
Hope this helps. Thanks for using FixYa.