1/4 mile is 402.336 meters, to be precise. What are 'approach bans'? In the US, helicopters may reduce the published visibility on standard instrument approaches by half, but not less than 1/4 mile or RVR 1200 (~366 meters), provided the final approach speed is 90 kts or less. ATC will never refuse an approach request, because it's up to each operator to know what the limits are for his operation, which are in the operations specifications from the FAA. And for non-commercial, Part 91 operations, the pilot is permitted to fly the approach regardless of the reported weather, and land if the in-flight visibility is found to be at or above the legal minimums.
You only need 200 feet visibility to see the approach lights at DA, because you're looking straight down at them, or very nearly so. And you can only descend to 100' above the touchdown zone elevation with just the approach lights in sight. In order to land, you must be able to see the runway environment, which includes a laundry list of specific items.
For those with sufficient interest and ambition, the pertinent part of FAR 91 is
here .