The absolute minimum requirements to commence training (through the usual route) are a minimum of 5 GCSE passes, at grades A to C , which must include Maths, English and at least one Science subject. These must be accompanied by at least two A-levels, one of which must be in a subject studied within the National Curriculum.
Those are the minimum qualifications before you can be considered for a 3 or 4-year university course. (In practice, many universities will be looking for 7 or 8 A-C GCSEs plus at least 3 A-levels with A-C grades).
There are other routes but these are generally for people with existing experience of higher education:
http://www.learndirect-advice.co.uk/helpwithyo urcareer/jobprofiles/profiles/profile820/
Chris