not sure, i have heard some bad things about MacMillan nursing, though when Mr Em was dying the nurse who came did a lot that the other nurses wouldn't do.
MacMillan nurses are generally employed by the NHS (with MacMillan providing funding for their posts for the first three years). They work across a wide range of roles, often in hospitals (although some work in the community). Their work is focussed on providing support for people with cancer in general (and not just on those who're terminally ill):
https://www.macmillan.org.uk/information-and-support/coping/getting-support/macmillan-nurses.html#46702
Marie Curie services are also purchased by the NHS. What you can have will depend on which services your local health comissioning organisation has decided to purchase.
McMillan nurses are usually senior sister grades with courses in both palliative care and a speciality. Most commonly ontology but there are some with specialities as well.
Marie Curie nurses may be qualified nurses but can be health care assistant level with additional training. The general difference is Macmillans advise and counsel, Marie Curie's provide care and support.