Readers may have heard about the recent plight of a postie whose case brings to mind the old principle that employees must personally perform their duties.

Tyrone Underhill began work with New Zealand Post in 2010.

On November 7, 2011, Underhill attended a team briefing.

Several matters were discussed, including the issue of unauthorised assistance on postie runs.

It was made clear that other people were not allowed to help posties perform their duties.

Underhill, it seems, did not heed these instructions and was assisted by his brother to deliver his mail on November 26, 2011.

His brother also happened to be a postie.

New Zealand Post took a dim view and Underhill was given a written warning.

A cumulative series of absences led NZ Post to dismiss Underhill. In part it relied on the warning given because his brother had performed his duties.

Underhill challenged his dismissal in the Employment Relations Authority which found that Underhill's dismissal was unjustified.

Unfortunately for Underhill, the authority also found that Underhill had contributed to his dismissal in several ways, including the unauthorised assistance of the brother. The remedies awarded to him were therefore reduced by 50 per cent.

One of the earliest cases to address the principle that an employee must personally carry out their duties concerned an actor unable to perform his role.

Frederick Terry was employed by Variety Theatres as the lead actor in a production of Sweet Nell of Old Drury, which was being staged at the Hippodrome at Portsmouth in southern England.

The play was to run for six nights, with one matinee, beginning in April 1926. Terry's contract provided that in the event of his non-appearance, he was to provide a deputy to the satisfaction of Variety Theatres.

In a stroke of very bad luck, Terry came down with a bout of pneumonia, pleurisy and dropsy in April 1926. He was unable to move for several weeks and at one stage it was expected that he would not live.

Terry was unable to perform at the Hippodrome and he arranged for an understudy to perform the role as was usual practice. Despite this, Variety Theatres cancelled the show and Terry was not paid.

Terry attempted to obtain the performance fees. When the employer refused, he was forced to take a claim in the courts.

The court had little sympathy for Terry. It found that because he was unable to perform any of the shows, Variety Theatres was entitled to rescind the contract.

Terry was unable to insist on another actor performing the entire contract in his place.

Terry's performance was the essence of the contract. The fact that Terry was absent for the whole engagement was significant. Perhaps if it had only been one night, it would have been a different outcome.

The cases of Underhill and Terry show that personal "performance" of services is fundamental to the employment relationship.

A doctrine enshrined in theatrical life in Portsmouth in the 1920s has rippled its way to one of the then-colonies in the 21st century. Such is the common law.