They would still be lawful. The status of the firearm does not change on June 30. June 30 is simply the date by which, in future, once the bill has passed both houses of Parliament and been brought into force, an owner would have had to be in possession of one in order to be grandfathered. People could still purchase them after June 30, but they would do so knowing that there would be no grandfathering, no ability to register it.
On June 5th, 2018. See this statement in context.