In continuation of what Raj Kumar has stated, I am compelled to add that engaging a car driver on retainership is only a fanciful idea of a person who reinvents the meaning of retainership for the purpose of labor exploitation. If I am correct, the terms "retainer" and "retainership" are not mentioned in any employment-related law. The dictionary meaning of "retainership" is "(of contracts or services, etc.,) having the property of retaining/retainment."
As far as I am aware, retainership is covered by the ambit of Service Tax and would be covered by the definition of yet another term not used in any labor law, i.e., "Management Consultant." Therefore, I am providing the extract of Section 65(37) of the Finance Act, 1994, which defines:
Management Consultant
"Management Consultant" means any person engaged in providing any service, either directly or indirectly, in connection with the management of any organization in any manner. This includes any person who renders advice, consultancy, or technical assistance related to conceptualizing, devising, developing, modifying, rectifying, or upgrading any working system of any organization.
Think for yourself where a car driver could be fixed on a retainer basis.