Paternity leave
In order to take paternity leave an individual must make a request to the employer 15 weeks before the expected week of confinement. The expected week of confinement is the week during which the birth is estimated to occur.
Other information due is the date when the leave will commence and whether one or two weeks of leave is being sought by the employee.
In your member’s case, the notice that he has given his current employer is indeed insufficient.
It might be possible to argue that your member was always an employee of the current employer and that the arrangement with the agency was a sham. However, this is often not easy to prove.
Given this, the best solution for your member may well be a negotiated rather than a legal one.