The Australian Twenty Pound note was only ever printed in 1913 and 1918, and the notes circulated from 1914 to 1938.
Depending on the signatories, an uncirculated note might fetch anything up to $495,000 AUD. A circulated note in good condition might fetch anything from $47,500 to 295,000 AUD.
A reputable coin dealer will be able to give a more accurate valuation.
Australia has never produced a Twenty-Five Pound note.
Twenty Australian dollars
The Australian Twenty Pound note was only issued in 1913 and 1918. An Australian 1918 Twenty Pound note (Cerutty/Collins), uncirculated and in absolute mint condition could fetch up to $495,000 AUD. If it has been circulated, but still in good condition, it might fetch anything from $47,500 up to $295,000 AUD. There were 421,500 printed. A reputable coin dealer will be able to give a more accurate valuation.
Your Twenty Pound note does not exist. Queen Elizabeth's parents had not yet been born in 1867.
Australian twenty-dollar note was created in 1966.
Australia did not have its own currency in 1907. The Australian Five Pound note was first issued in 1914. The Australian Five Dollar note was first issued in 1967.
The first Bank of England Twenty Pound note was issued in 1725. The first Bank of England decimal Twenty Pound note was issued in 1970.
There was King George V and King George VI. To get an estimate of value on an Australian predecimal banknote, you will need to provide the two signatories on the note and the serial number.
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The modern Fifty Pound note was introduced into the currency in 1981 to keep pace with the times and inflation. The introduction of a higher value banknote, such as the Fifty Pound note, relieves the pressure on the smaller banknotes such as the Ten and Twenty Pound notes. This means that the Ten and Twenty Pound notes will last longer in circulation and become relatively cheaper to produce and maintain in circulation due to a reduced demand for them.
There was no Australian Dollar until 1966, long after the "early settlement". At the time of currency changeover from Pounds to Dollars, the Australian One Pound note converted to the Australian Two Dollar note.
A Bank of England 1912 Twenty Pound note (issued by London or Manchester), circulated but still in good condition, might fetch anything from £900 to £4,000 GBP. A reputable coin dealer will be able to give a more accurate valuation.