Buying a return ticket but not specifying a return date (within a year) from UK

Hi,

I want to fly from the UK to Australia at the end of the year.
Obviously, I would be selecting the date I fly out but would like to be
flexible on the date that I return.

I have heard that you can get a return ticket that does initially
require a return date. I am aware that you cant just stroll into the
airport and fly without notice but would imaging that you give a short
notice.

Does this type of flight exist or am I way ahead of my time and should
return to the real world :-) If so, do many flight operators offer it?
How does it work? Will it save me a substancial amount on buying my
flight 30 days prior to leaving?

Cheers

Burnsy