Retrospective Regularisation Of Contractual Employees

Sabyasachi Ghosh: Temporary on contract basis appointments ware given after obtaining name from employment exchange and following the regular process of selection. Initially the appointments where for 6 months but continued for 20 years uninterruptedly. Appointment was against the vacancies created by the adhoc promotion of existing regular employees to the higher posts who enjoyed their promotion till their retirement. The contractual appointment, said above, was with pay scale and increment. The question is, whether such appointments, as per rule, in such a sanctioned vacancies, can be regularised retrospectively? please provide links of case reference of High Court and Supreme Court.