If you falsely represent that you have a patent when you do not or if you represent that you have applied for a patent when you have not you open yourself up to liability which will may well result in on summary conviction a fine.
No offence is committed if the representation is made in relation to a product or process in respect of which the relevant patent has expired or been revoked, and before the end of a period which is reasonably sufficient to enable the accused to take steps to ensure that the representation is not made or does not continue to be made.
Are there any defences available? Yes. You can raise a defence if you can prove that you have used due diligence to prevent the commission of the offence.