That thunderstorm really tested our drains… to the limit.
It was my sad duty to wrap my arm in rubber glove and bin liner and stick it down, pulling out the many years of detritus that has caused the blockage and associated flooding.
It now drains, and thanks to improvisation (8″ flower pot) we now have a good filtration tank which sits on top of the hole and filters out any cack which might end up down there, plus I’ve put pebbles into the rain gulley to allow water to get through but prevent crap from running through.