A householder does not have any rights over the area of highway adjacent to their property. If vehicles are legally parked and not causing an obstruction then they are entitled to park there, even though it is outside your house.
If long term parking occurs from local businesses, hospitals, shops, universities or colleges.
It may be possible to introduce restrictions on parking. Assessment is required by a highways officer.
Very little can be done if you can't park at school opening and closing times due to parents parking because it is a short term problem, occurring twice a day during term time. Parking restrictions are usually ignored by parents. Any restrictions put in place can often be far more restrictive on residents than on parents dropping off or picking up their children.