allow/give somebody (a) free rein
to allow someone to do what they want or go where they want to (often + to do sth) The older kids were given free rein to do whatever they wanted. We shut the kitten out of the bedroom but allowed her free rein in the rest of the apartment.
allow/give something (a) free rein
if you give ideas or emotions free rein, you allow them to develop and do not try to control them With all these materials available, we can give our creativity free rein.