In the new version of pywbt, I made a breaking change that should make running Whitebox workflows much easier without having to deal with temp files and such. Please check the examples which is the same uk region that we were working with. It's now available on conda forge, too.
usage: https://pywbt.readthedocs.io/latest/#usage
uk example: https://pywbt.readthedocs.io/latest/examples/basin
Also, check out the example utils module. I made some modifications to nasadem (takes care of the buffer issue that I mentioned) and vectorize functions:
https://github.com/cheginit/pywbt/blob/main/docs/examples/utils.py
Delineate Basins - PyWBT
by @cheginit