New entrants are likely to be graduates of any discipline.
Most agents enter with previous experience in publishing, for example as a commissioning editor or a rights manager. The Agents' Association (Great Britain) has a useful website which allows a search of agents across Britain.
You would need general administration skills, and you may find it useful to have qualifications or experience in areas such as word processing, book-keeping, public relations and marketing.
A degree could be an advantage, although not essential. Relevant subjects include arts management, arts administration options in other arts-related degrees and business studies, but relevant experience is more important than having a degree.