Coventry also give multiple aircraft the same squawk, 4650 for VFR and 4651 for IFR. I understand this is for the benefit of Birmingham, who control the overlapping airspace, as Cov have no SSR of their own.
It's also my understanding that you can request and receive a radar information or even a radar advisory outside class A or D airspace. Whether you get it or not is subject to ATC agreement and ability to do so. If not, I've been hoodwinked for a number of years now.
I can't actually think of an occasion when I've NOT been given "radar control" when crossing class D, even when VFR. I always accept (because otherwise ATC will probably ask for the present heading and give the reciprocal to vacate the airspace).