Paul. Certificates don't actually expire unless you are on the RTITBs NORS database when they expire after 3 years. The requirement to have forklift operators trained falls on the employer in law not the employee, (section 2 c of the HASAW Act). You are free to refuse to do anything at work including driving the truck but I can't say what the employer's reaction would be. It is the employer, not you, who would get prosecuted under these circumstances in the event of an accident.

It is your employers responsibility to sort out refresher training for their employees.
Although it is not a law that you carry out refresher training it is just advisory by the ACOP Manual to carry out training especially if employees have had an accident.