The Government’s testing regime has come under pressure in recent weeks amid reports testing centres have been overwhelmed by demand.
Mr Williams said: “[Moonshot] is an opportunity for Royal Mail to show what we can do after the rapid change of the postal market in 2020.
“We have challenges, but we have a fantastic opportunity here too in the growing customer demand for parcels. If we can adapt our business quickly enough, we will be well positioned to meet our customers’ demands for more and more items, to and from more people, delivered more frequently.
“If we don’t, the market will move away from us and we will be consigned to delivering a reducing volume of letters and struggling to meet demand in the growing parcels market.”
Mr Williams’ transformation ambitions received a boost this weekend as Royal Mail’s biggest investor, Czech billionaire Daniel Kretinsky, said he “fully supports” the need for an immediate change.
Royal Mail was plunged into crisis earlier this year with the abrupt departure of boss Rico Back after less than two years in the job.