You are asking only part of the correct question, because playing music in a workplace is still covered by the Performing Rights people. A workplace normally requires a PRS licence, but there are few concessions (for your employer) if the music is played, one of which is the following: -
"Personal portable devices - Where music is only used in the workplace by individual employees or workers solely by means of personal portable devices (such as MP3 players) with headphones. Any music must only be audible to the employee or worker to whom the personal portable device belongs through a headset attached to that device and not to any other individual in the workplace."
So individual headphones only