The Party Wall etc Act normally only applies if you are:
Excavating within 3m of an adjoining owners property and to an assumed greater depth than their foundations.
If you are building on a line of junction
If you plan to alter a party wall by cutting into it, extenting it, removing it etc.
Assuming your garage simply abuts next door and other otherwise strucutrally sound and water tight, you can dry line the party wall and run any services behind the (insulated), hence no cutting into the party wall is required.
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