Car makers use extra thin oils to get the last fraction of a % fuel efficiency from engine, not because the thinner oil protects better, maybe if I lived inside arctic circle I would use it in winter.
Thinnest I will use is 5W30 in cars but my highly stressed Japanese motorbike engine uses 10W40 ( recommended by Suzuki ). Some better quality thinner oils have molybdenum compounds in them to improve wear.
Normally the hotter the climate the thicker the oil, and Italy is hotter than UK for sure.
You sound as though you think castrol 5W30 will damage your engine, it certainly will not and will arguably protect it better.
Honda set the 0w20 as the better choice for quite all its petrol engines, Civic Type R included. Since 2001 in European, Australian and Japanese markets, Honda petrol engines are prefilled with a 0w20 (Bardhal, Castrol or Idemitsu) for every climate condition. Since 2009 the 0w20 is prefill oil also in US market, leaving the 5w20 used before as the thinner oil was not easily avaiable. Note that also in the USA the 0w20 is the best choice if you're running along deserts in Arizona and New Mexico, but also in Alaska... Climate doesn't matter for this engines, and anyway Italy is not so hot to suggest different oil viscosities.
No, I'm not worried about the possibility of damage from the 5w30, but I'm sure that those latest Honda engines are better protected by a 0w20 than a 5w30: I think that the 30 number could be better in very strong usage, circuits or german highways with many minutes at very high speed, but the 0w is definetly better in cold starts and city usage with start&stop set on. Thinner oils are better in this kind of usage, because they are better pumped also at low revs and they can reach more easily small parts and small volumes of the engine. Sure, the engine must be designed and built for low viscosity oils, I would never use a 0w20 in a 1.4 Fire Fiat.. but Honda engines are ok for 0w20 since 2001, so why not??
More, since 2013 Honda Hybrids use a 0w16 (I-DCD, I-MMD)... as I wrote before, engines running and stopping lot of times enjoj low viscosity oils, that's why Honda is testing a 0w8...
Anyway, my "question" is different... Why Honda does not offer the best oil for its engines in our italian workshops, providing a common and cheaper 5w30? IMHO the official service net should offer "something more" than a generic workshop also considering they are not cheap, otherwise there are no reasons to go there...