An employee is someone who has a contract of employment. All employees are workers, but an employee has extra employment rights and responsibilities that don’t apply to workers who aren’t employees. Employees are entitled to statutory sick pay, maternity, paternity and adoption leave, and shared parental leave. They have protection against unfair dismissal and the right to request flexible working and to receive statutory redundancy payments.
Engage is a phrase used by employers to take on either sub-contractors or workers. They are usually engaged for work for a fixed period.