MJ,
EU Member States may make regulations going beyond the requirements made under EU-OPS. Regarding the UK (applicable to aircraft registered in the UK) the national authority (CAA) may direct operators, in the interest of safety, to carry in addition to the minimum required crew members such extra crew members as specified in any such direction -
C.f. Air Navigation Order 2005,
Art. 25(15).
A similar provision is bound to exist in equivalent national legislation across the union. Your Ops exam concentrates on EU-OPS however and national practices (of the state regulating the exam) are relegated to Air Law.
EU-OPS does not (yet) require operators to carry cabin crew members on board aircraft with a maximum approved passenger seating configuration of equal to, or fewer than, 19.
Refer to
EU-OPS[¹
][²
] :
OPS 1.990 - Number and composition of cabin crew
(a) An operator shall not operate an aeroplane with
a maximum approved passenger seating configuration
of more than 19, when carrying one or more passengers,
unless at least one cabin crew member is included in
the crew for the purpose of performing duties, specified
in the Operations Manual, in the interests of the safety
of passengers.
[...]
-----
OPS 1.990 - Numero e composizione d’equipaggio di cabina
a) L’operatore non deve impiegare un velivolo con
una configurazione massima approvata di posti passeggeri
superiore a 19, se trasporta uno o più passeggeri, a meno
che nell’equipaggio non sia presente almeno un membro
d’equipaggio di cabina incaricato di svolgere compiti legati
alla sicurezza dei passeggeri e specificati nel manuale delle
operazioni.
[...]
----------
[¹] COMMISSION REGULATION (EC) No 859/2008 of 20 August 2008
amending Council Regulation (EEC) No 3922/91 as regards common
technical requirements and administrative procedures applicable to
commercial transportation by aeroplane - Annex III ("EU-OPS")
[²] Versione italiana.