Thank you Alan and Mark, that's very reassuring. I've had a close inspection this morning and , in places, some of the edge of the ditch has been dug away taking the snowdrops as well, but they must be still there somewhere and I am comforted to know they will recover. At one end of the ditch an attempt has been made to level the ground by spreading the surplus over a larger area so it is only about six inches deep and more manageable.
Final question, does anyone know of an easy way to extract wellies stuck in 15 inches of mud? Luckily my feet aren't still in them!