Right first thing you need to do is ascertain if the wet patch on the front of the property is anywhere near where your overflow/warning pipes for the loft terminate to outside.
If yes quite likely your culprit and we can look at causes
If no then you need to see what else is nearby or potentially terminating into the gutter. Is it just the gutter blocked and overflowing and it’s just an unfortunate coincidence.
If it is the overflow then either the tanks are overflowing or something is backfilling causing the tank to fill. I’d say that’s the likely culprit.