A programme extension can be recommended where a student cannot complete the programme within a normal timescale because of exceptional circumstances. If you find yourself in this situation, talk to your supervisor.
If you are academically unsatisfactory the Board of Studies can recommend that your programme is ended before its normal end date. This may be due to reasons such as poor attendance (without good reason) or through having failed so much of the programme that it is no longer possible to graduate.
Further information can be found at www.york.ac.uk/students/support/academic/taught/programme/
Also, see 'Exceptional Circumstances Affecting Assessment' for any other circumstances which may affect you undertaking any assessments.