Salaam to you Samiun,
"And He who sends down (from time to time) water from the sky in due measure, and We raise to life therewith a land that is dead. Even so will you be raised (from the dead) (Surat az -Zukhruf, 11)
It's not about the size of the rain drops that matters. When there is just too much of it, there will be floods. I guess it has more to do with the natural topography. Low and flat lands will be more susceptible to floods.
Yes, Britain may be an advanced nation but some of its infrastructure were made a very long time ago indeed. While most of Europe had to rebuild itself after the war, Britain didn't and still carried on with its old infrastructure.
I always wonder how does Europe(particularly Britain) sometimes get flooded when the rain is sorta like drizzling when it's supposed to be raining heavily? Here in south-east Asia, the rain is very heavy and of course we have many areas flooding the rural areas of a state. I just couldn't fathom the idea of flood happening in some parts of UK when it's good and advanced with it's drainage system.. Subhanallah..~