Is this not how second waves begin?
if you have any evidence to support it - please post. I suspect you're guessing though to promulgate fear.
Those that travel to Spain will be risk adverse by the very fact that they are prepared to fly. Come nightfall the streets will be full and people will soon forget social distancing even if it was possible as they try to have a good time.
You do realize that the WHO guidance on 'social' distancing is 1m don't you? You also realize that the WHO guidance relates to indoors rather than outdoors? God only knows why the UK government (almost uniquely) decided to say 2m instead of 1m and in doing so rolled a whole load of viable businesses over the end of the cliff.... and scared the crap out off the unthinking population, many of whom would now quake in terror at the prospect of standing 1m next to a stranger even though the WHO says it's a safe distance. Boris is going to have to answer some hard questions (to which he will trot out the usual cliches and bluster).