I actually think it's the batting that makes the most difference. don't know what's available in the UK, there are lots of members who live there and hopefully someone will chime in with a cotton batting (wadding?) that will shrink a bit and is available there.
I also have a theory that if you pre wash (pre shrink) your fabric and don't shrink your batting you get more wrinkles. You quilt the fabric to the batting which holds it in place. The batting shrinks, but not the fabric which has to bunch up a bit to accomodate the smaller batting. If your fabric also shrinks because you didn't pre wash, it will shrink at about the same rate as the batt, resulting in a smoother quilt. That's my theory anyway ;-)
It's sort of trial and error. Try different battings, flannel pre wash/don't, tumble dry vs. air dry etc. eventually you will come up with a combo that you like.