@MarkD, you must have stumbled upon some old instructions - please give me the link so that perhaps it could be fixed.
Forums aren’t great for finding up-to-date information - there is a lot of outdated/incorrect info around here.
Please follow the official instructions here and it should work: https://github.com/fastai/fastai/blob/master/README.md#conda-install
torchvision-nightly was needed only back in Nov-18 and is no longer required.
If you encounter a problem please post here: Fastai v1 install issues thread