The job of a bookkeeper requires a certain set of skills and as you gain experience you will find a number of other opportunities may arise.
There is no legal requirement to have a certain qualification to be a bookkeeper, but if you are looking for employment in this area you will often find that you are more likely to be accepted for a job if you do. Most people start off by doing a bookkeepers or accountancy course at college. You will usually need to have 2 or more GCSEs at grades 9 to 3 (A* to D) for a level 2 course.
You can train yourself to become a bookkeeper or learn whilst on the job, which will allow you to keep study costs down and work at the same time but if you are planning of becoming self-employed then it is important that you ensure you know exactly what you are doing before offering your services to clients. You may have some family members who are self-employed and you may start off by doing their books for them. This will also give you experience that you to add to your CV to make you a more viable candidate when it comes to applying for jobs.