To work in a primary or secondary school as a qualified teacher you should have Qualified Teacher Status (QTS). If you are a graduate, this is usually achieved via a one year Post Graduate Certificate in Education. There are also part-time and flexible PGCE courses available.
If you are an undergraduate then you can complete a Bachelor's Degree with QTS in either 3 or 4 years or do a non-teaching degree followed by a PGCE.
For information on training to become a teacher contact the Department for Education. They can provide information on entry requirements and on local providers.
If you do not have the necessary entry qualifications then you might like to contact Croydon College who offer access to teacher education courses.