Bandera europea

[cónsul scipio]

No obstante, y como ya se ha dicho (Ley 14/2014, de 24 de julio, de Navegación Marítima.)

2. Los buques extranjeros, salvo los de guerra, enarbolarán, junto al suyo, el pabellón español, conforme a los usos marítimos internacionales.

y... si es según los usos marítimos internacionales os hago copy pegui de la etiqueta inglesa:

Foreign or courtesy Ensigns
It is customary, but not obligatory, when lying in a foreign port, to fly the maritime Ensign of the country being visited, as a mark of courtesy. The courtesy Ensign is usually considerably smaller than the vessel's Ensign and it would appear to be custom for it to be struck at the same time as the yacht's own Ensign, although opinions differ on this point.
The Ensign should, in the case of a single* masted vessel, be flown at the starboard topsail yard, or upper crosstrees. In the case of yachts with more than one mast it may be flown either at this position or at the fore or mizzen masthead. But, whenever it is flown, care should be taken that it is not hoisted at a position inferior to any other flag except the yacht's own national Ensign and club burgee or, in the case of a yacht club's flag officer, the flag officer's personal flag.
The British maritime Ensign for use as a courtesy Ensign is the Red Ensign and not the Union Flag.