Production roles:

 

A creative producer is basically the Director they speak to clients and to find out what production budget they have, what there target audience is and ask the client what is to said in the advert and what music or jingles are used, they also over see most of the production that goes on.

A copywriter is required to write all the scripts for radio commercials, they're job is to make sure the script they write keeps the audiences attention, some copywriters may have a background in script writing and sometimes they  are both copywriter and producer.

A voiceover artist is required to use their voice and read the script which they are given, the voice over artist will usually be trained as radio adverts require someone with a clear voice in order to keep the audience’s attention,in some adverts like the go compare on  a session vocalist is required to do the singing parts of the advert.

A recording engineer is required to record music speech and make sound effects for radio adverts, they are must be able to use different electronic equipment and be able to produce high quality radio adverts. 

http://www.thevoiceovergallery.co.uk/ Here a link to a well-known voice-over company that is based in Manchester.