How long do you give someone to sign a contract before they are no longer considered an employee?

A couple months ago they shifted an employee’s contract to zero hours and changed his job title. He signed it, then said he wasnt given the chance to do the new role he was promised and was upset that it was moved to zero hours. But he signed it. The company then reverted the role title but kept him on a zero hour contract, and he refused to sign it. It has been 2 months since the contract with his reverted title was sent out.

So this is quite muddied water because the employee is on a zero hour contract. He hasn’t been working for the company, and all the company did was change his job title to describe his role better. He says he wants to go legal, so how long do we have to wait before he is no longer considered an employee since he doesn’t want to sign the contract?