Where a vacancy arises because an employee leaves, but this occurs after an earlier redundancy exercise, is the employer obliged to offer the vacant position to one of the individuals who was made redundant?

No. The employer's duty to consider alternative employment for a redundant employee ends on the termination of his or her employment. It is good practice for employers to keep in touch with employees dismissed for redundancy with a view to notifying them of any vacancies, but there is no requirement on them to do so.