Probably not the best back nine in England, but still a wonderful surprise is the back side at Hillside, adjacent to Birkdale, which may be as good as either nine at its neighbor. The reason it is such a suprise is because the front side is relatively nondescript.
It doesn't get a lot of love on here, but if you were to ask a cross-section of serious golfers in northern England for their pick as the course with the best back nine, most would say Hillside.
It plays through spectacular terrain but, in common with many links courses, there is just not enough spectacular terrain to accommodate 18 holes. Hence a rather dull, flat front nine which accentuates the drama of the back.
Another example of this - albeit a couple of notches down the quality scale - would be Prestatyn. It starts with some rather unmemorable flat holes (and some convoluted internal OOB) before being lifted to real quality in the dunes on the way home.
This phenomenon is not limited to the coast, either. Mottram Hall in Cheshire is a resort hotel course with a dull front nine on a flat field. Its back nine however, on fabulously undulating land behind the hall, is terrific with some holes that would be highly regarded by the most discerning of GCA nerds.
I guess that if you've only got enough land for half a good course, it makes some sense to save it for the back nine. I tend to prefer the approach taken at Wallasey however, where the dunes are visited several times in the round, interspersed with periods on less exciting ground.