Thanks for the reply Ana.
The socket on the laptop is a single 3.5mm TRRS standard headset / headphone socket. The laptop is a new Dell Latitude 5500 series with the latest windows 10 updates. The Realtek (R) Audio drivers are the most recent update available.
The inbuilt laptop microphone is working. The headset and microphone work on other devices.
My problem is that the headset, and its microphone, are not recognised properly by the system. The Realtek driver seems to have identified the headset as a headphone and there doesn't seem to be any way to correct this. Previously when a device was plugged in Realtek generated a popup to ask what the device was. This no longer happens. The audio manager previously allowed the user to correct the identification of a device. This facility seems to be missing as well in the latest update.
Is there a work around to get the popup to appear - not ideal but would at least address the immediate issue - or to get the audio interface manager? I realise these may be Realtek driver issues