C.M., welcome to the forum, I forgot to say that at the beginning.
You have me perplexed a bit. The whole idea that you'd need somebody's clearance to start emergency descent is completely out of this time-space continuum. I do not think that's what you ment, but without a reference it is hard to discuss.
Current AIB procedure here:
NhMm.png
AIP Germany: did not check, not available online f.o.c.
LIDO eRM CRAR Germany: nothing there and I assume the publishing house does have that one right
FCTM: not in the latest...
What you may have seen is a re-location of the ATC ... advise item in the procedure flow, which happened around the time FCOM went digital. But that whole PNF loop was cancelled altogether.
The main reference would then be
ICAO Doc 7030 Regional Supplementary Procedures - EUR para 9.1.1 and 9.1.2.2.(b)