You must get permission from the MCPS (Mechanical Copyright Protection Society), it is they who will issue the licence to use the work.
They will give you the writer & publisher details if you don't already know them. It is important to make sure you have the correct writer for the song as sometimes there are two or more songs with the same title.
You must also have all writer and publisher details credited on the CD sleeve/booklet.
For a specific number of CDs to be pressed they will be able to tell you the amount that you must pay for the relevant tracks. This relates to the number of CDs, the number of tracks on the album, the lenght of each track and the retail price of the CD.