Even Turkey is doing temperature checks on international arrivals. If PAX returning from Spain are to be quarantined then they must be checked at arrival and have a contact tracing app. Of course, none of this would have happened if the youngsters had obeyed the social distancing rules in the first place, France will be next.
In these countries where cafe culture and all hugs and kisses are the normal we may as well just accept the fact that no matter what the official advice, they will always do their own thing. A brutal regime like Turkey enforces the rule in the main tourist cities, hence the Eastern provinces being no-go areas, the Med countries must either do the same or face the economic hardship of their laissez faire approach. Sadly, once again, the UK aviation industry will be hit hard.
Police have already stated they do not have the resources to enforce quarantine and there is no real way of checking where people are without location technology.