I have checked with our service manager and the issue affecting SWR and GWR is not with Darwin, but with connectivity to Darwin. I understand the relevant suppliers on both sides are working on understanding what is causing the connectivity issues. It appears to be affecting all LICCs (as noted above other consumers do not appear to be suffering from the same problems - that we know of at least) but for as yet unknown reasons it is affecting the SWR and GWR LICCs more than the others, which is why those TOCs have chosen to temporarily disconnect completely from Darwin until the issue is resolved.
I will endeavour to post updates on progress towards resolving the issue as and when I can.