The NSW Liberal party has been slammed by election funding authorities for "concealing" the identities of illegal major donors before the 2011 election that brought it to power, including via the secretive Free Enterprise Foundation.

In an extraordinary finding, the NSW electoral commission has concluded that, based on evidence given to the Independent Commission Against Corruption in 2014, the foundation was used by senior Liberal party officials to "channel and disguise donations by major political donors some of whom were prohibited donors".

Funding scandal: Cabinet secretary Arthur Sinodinos. Credit:Andrew Meares

The commission says it has relied on evidence given to the ICAC by senior party officials including about the "involvement" of current cabinet secretary Arthur Sinodinos, who was finance director and treasurer of the NSW Liberals at the time.

In a statement released late on Wednesday, commission chairman and former NSW court of appeal president Keith Mason, QC, says the NSW Liberals have repeatedly failed to hand over details of donors to the foundation, which in turn helped bankroll the party's election victory five years ago.