Answer ... Patents are unenforceable if they lack any of the necessary requirements for validity.
A patent may be unenforceable if it has been obtained by fraud or false suggestion. A false suggestion, which would normally be expected to be made to the Australian Patent Office during prosecution, need not be wilfully false. If the representation was false and was material to the application securing acceptance, then the patent may be held invalid.
In some cases, if a patentee has a claim that is knowingly invalid and there is an undue delay in making a corrective amendment, then the court has the discretion to refuse that amendment. This, in effect, can tie a patentee to an invalid claim that cannot be corrected and is thus unenforceable.
Innovation patents proceed to grant without substantive examination. They remain unenforceable until such time as they have undergone substantive examination and have been certified.
Answer ... As mentioned, in Australia, a patent may be held to be invalid if it is shown that the patent was obtained by fraud, false suggestion or misrepresentation.
For false suggestion or misrepresentation, it is not necessary that the person making the statement knew that it was false or deliberately sought to mislead. All that is required is that the statement was material in getting the patent granted and was not factually correct. Statements of advantage in the specification made in good faith are unlikely to be problematic (Uniline Australia Ltd v SBriggs Pty Ltd  FCA 222 (16 March 2009)). However, statements made in the specification implying factual experimental support where none such existed (Morellini v Mizzi Family Holdings Pty Ltd  FCAFC 13) have been sufficient to get a patent revoked.
Statements made during prosecution can also lead to a patent being considered to have been obtained by a false suggestion or misrepresentation. (Ranbaxy Australia Pty Ltd v Warner-Lambert Co LLC (2008) 77 IPR 449). The representation must have materially contributed to the patent getting granted, although it need not have been the only factor in getting the patent granted.
The courts have quite broad powers and it can be shown that a party engaged in patent litigation acted with ‘unclean hands’, which can be reflected in the decision and the remedy.
Answer ... There is no duty of candour comparable with that in the United States and no ongoing duty to keep the Australian Patent Office apprised of search results. However, as mentioned above, if an applicant presses or maintains a claim that it knows to be invalid, then ultimately the court may deny it the opportunity to make corrective amendments.
There is also no formal doctrine of file wrapper estoppel. However, if a patentee later makes assertions in relation to a patent that are inconsistent with those made during prosecution, then the question of misrepresentation and the materiality of that to the decision to grant may apply.