As a serving officer I can tell you that all police forces require that you join at the rank of Constable (excluding forces where cadets are utilised), and that you complete a probationary period, currently set at 2 years.
There is no requirement for formal qualifications to join the Police Service in England and Wales and there is not "fast-track" scheme for graduates wishing to enter at a higher rank. There is however a High Potential Development Scheme (HPDS) aimed at those officers who have the necessary skills to become managers and whose specialist skills could be utilised more effectively etc. Again though, you need to successfully complete 2 years probation and even then, a degree will not guarantee you a place on the scheme as it is available to everyone upto the rank of inspector I think.