You will need a high level of design skill and creative vision, as well as practical sewing skills.
In practice, many costume designers have a BTEC HND, degree or postgraduate qualification in costume design, fashion, theatre design or performing arts (production). Check exact entry requirements with course providers.
Alternatively, you could start as a wardrobe assistant or costume maker and work your way up to designer as you build experience and contacts in the industry.
You can get relevant experience through: student theatre and film productions; amateur theatre; working as a costume ‘daily’ (a temporary helper) on TV or film sets; casual wardrobe work in theatres; working for a theatrical costume hire company.
You may be able to start in the film and TV industry through an apprenticeship-style new entrant training scheme, such as the BBC's Design Training Scheme. Competition for places on this type of scheme is very strong, so you should still gain practical experience as explained above before applying.
Whatever your qualifications, you should find practical work experience and build a good portfolio or 'showreel' DVD of your design work to show to potential employers.
Major broadcasters and regional screen agencies sometimes run their own new entrant training schemes – contact Skillset Careers for more information. Competition for places on training schemes is very strong.