Generally, an ICC is required when navigating the inland waterways
of Europe; the main notable exception is The Netherlands. In Holland an ICC is only required by vessels that are either longer
than 15 metres and/or capable of more than 20 kph (~ 11 knots).
If cruising to Europe to explore the canals and rivers, both
categories 'coastal' and 'inland' will be required and so the CEVNI test, as well as proof of general boat handling competence,
is needed.
It should also be noted that most European countries insist that
vessels navigating their inland waters carry a copy of the relevant local rules.
For France, The RYA Book of Euroregs for Inland Waterways suffices,
but it does not for Holland or Germany.
Those countries insist that their own publications, written only
in their native languages, are carried.
It is probably advisable to also carry the Euroregs book so that there is an English version of CEVNI
on board.
For coastal areas in Northern Europe and Scandinavia, the ICC
is generally not required.
Again, there are exceptions and these include Poland and the
Baltic States of Lithuania, Estonia and Latvia.
It is also useful to have one in Germany. Conversely, in the Mediterranean an ICC is usually required,
particularly in Italy, Greece, Croatia and Turkey. ICCs are not required in Spain on British flagged yachts.
However, Spanish harbour masters and other officials are used to their own nationals having to be licensed
and so can be difficult to persuade that British flagged vessels do not require them.
You either have to be prepared to stand your ground and argue the case or you may decide that it is easier
to actually have an ICC. Portugal does require skippers to hold the ICC.