Answers:
What does a runner do?
He/she is the lowest rung of the chain in a production team and will do a range of jobs such as getting teas and coffees, driving people around, fetching carrying and basically helping out in a wide range of ways.
What are the different roles of the people working on a live tv programme such as The Voice?
There is no quick and easy answer to that question. There are literally hundreds of people involved; in production, crew, technical, facilities, post production etc etc. You need to read up about the different roles in a television team.
How hard is it to get into this industry?
Very, very hard indeed. But harder than that, is to make a career in it over a long period of time. Most people do not get in, fewer make a good living, even fewere retire after a lifetime in the industry
What qualifications would I need? And would I need media based A levels to get onto these courses?
Nothing specific. No you don't need to do media based A Levels. Do the most academic subjects you can do to the highest level you can. Qualifications are way less important than experience.
Do you need to be creative (I'm really not)?
No. Or rather no more than in any other field of work. everyone is "creative", even you. People in TV are not necessarily more creative than anyone else. It is a trade and a business, it is not an "art".
Beware though - live TV stdios in production are very seductive places. They look glamorous and fun, and they can be. But there is also a lot of hard work going on behind the scenes, non-glamorous and tough, behind the scenes. It may look fun, but there may well be better career paths to follow!