It all depends on the group. We've even had members in our group who hadn't completed their PPL and many who have joined shortly after getting PPLs. Typically, the insurance company wants a conversion signed off by an instructor, and sometimes an extra premium is payable by the new member as a one-off. There has never been any extra to pay by the time the insurance is renewed. I don't recall them ever increasing the excess for a new member. Our newest member should complete his licence in the next few weeks.
I've certainly not noticed any slow-down in the sale of group shares in the North Midlands. Things may be different in the South.