I completely understand your reasons for wanting to leave Adelaide and why you are considering a return to the UK. I too am from the North of England and I would like to return although I do worry what I would return to. Personally I would stay to get citizenship - at least you can always return in the future. A move interstate is a big thing to do if you are not sure, it would mean uprooting your children again.
If you do decide to return to Manchester, keep us updated. It does seem a bad time to return to the UK at the moment , although a lot of people seem to be doing it.