Official references to intra-EU cash declaration seem to be vague and lacking. There is no mention on either of these
EU or
UK government websites. All information seems to pertain to cash entering or leaving the EU. The only reference that I could find to intra-EU declarations is in this
FAQ, which then unhelpfully links back to the first link I provided.
It's certainly news to me that one would have to declare amounts over €10,000 when travelling within the EU.