Hold on to your hats, because the facts are frankly, amazing.
Here are the Top 10 years of tax to GDP ratios since 1980-81and the government in power at the time:
2004-05 24.3% Liberal
2000-01 24.2% Liberal
2005-06 24.2% Liberal
2002-03 24.0% Liberal
2003-04 24.0% Liberal
2006-07 23.7% Liberal
2007-08 23.7% Liberal
1986-87 23.3% Labor
1987-88 23.2% Labor
2001-02 23.2% Liberal
(Note: The Turnbull government gets an award for the next highest with the projected tax to GDP ratio of 23.1% in 2018-19).
Even more extraordinary are the facts of the 10 lowest tax to GDP ratios since 1980-81. All 10 are under Labor governments. All 10.
Here they are:
1992-93 20.0% Labor
1993-94 20.0% Labor
2010-11 20.0% Labor
2009-10 20.2% Labor
1991-92 20.7% Labor
2011-12 20.9% Labor
1983-84 21.0% Labor
1994-95 21.2% Labor
2012-13 21.5% Labor
2013-14 21.5% Labor
And the source for these numbers are the MYEFO released by Treasurer Morrison and Finance Minister Cormann in December 2015: https://www.budget.gov.au/2015-16/content/myefo/html/index.htm