Miserable, petty nimbys. Amazing that people can nimbys when their b.y. Is a de-sanctified garage?
They can, however, be shut down more straightforwardly by the Environment Agency who (bless 'em) define anything washed off a car (even if you are using only the finest and purest glacial meltwater and no detergent) as effluent which cannot be permitted (commercially) to enter surface drains (along with all the other "stuff" that's washed off buildings and roads by the rain). Yes - this is nonsense also
It is, of course, highly likely that the site does have an intercepted drain (as it was a filling station forecourt) but I doubt anyone has had it maintained/pumped out since it was decommissioned.