a while since my last post on this one..... the update is ..... it turned out to be red mite which multiplied rapidly.
Various tactics have been used including the Barrier Hygiene powder, squashing any clusters that appeared with rubber gloves on (yeuch - but strangely satisfying!), clearing out and burning bedding, power washing the house (with the chooks out - ha ha) and squashing any of the little blighters as they came out to avoid the water.
Think its under control now tho i'm told they probably cant be got rid of completely