Training a Police Officer is an ongoing procedure, many officers now have a degree, with much of the recruitment coming from graduates programmes. Police recruitment assessments are not easy and to suggest that being a teacher is somehow more valuable simply because they do a degree is disingenuous. Also a PCGE can be done whilst working, through schemes such as the School Direct or SCITT programs which pay a bursary of up to £20k in support or through a salaried system for those with relevant experience outside of teaching. There are also schemes (at least one that I knew of) that mean ypou can become a QTS without a degree if you have other skills and qualifications.
So you can become a teacher with a 3 year degree and then work while obtaining your one year (2 years if p/t outside of a school environment) PCGE.
Not much different from many other comparable professions such as accountancy for example.
Accountancy is not a comparable profession