Packer changed his mind after coming to Canada, and has discussed this in a number of his books. Here's the most charming and compelling quote explaining his reassessment of the charismatic movement (from Rediscovering Holiness at 62):
What should one say of the worldwide charismatic movement of the past thirty years?...I believe that God has generated it in order to counter and correct the death-dealing fashions of thought, which, starting with theologians and spreading everywhere, for the past century have done damage by demurring at the truth of the Trinity, diminishing the deity of Jesus Christ, and for practical purposes discounting the Holy Spirit altogether.
To deal with these theoretical errors, and the spiritual deadness to which they have given rise, God has raised up this movement of uninhibited and flamboyant Holy Spirit life...Those who maintain the errors mentioned are thus comprehensively outflanked, not to say upstaged. How wise is the strategy of God!