The raised bed is lined with plastic round the sides - 2 sleepers high, and the soil beneath was heavy clay, not a great help with drainage. It won't be easy, but I feel that my best bet is to remove the plastic?
If the plastic is at the sides-I don't think that will make much difference to the drainage
The puzzle at the moment is the silvery bits-am stuck-perhaps you could post a picture?
If the soil beneath is heavy clay, you could do with breaking the surface up and adding a 4" - 6"layer of shingle and coarse gravel beneath the soil. What sort of soil did you put in the bed?
ALDI compost is fab!! cheap too, and we are very happy with it.