If I plug these into my PC’s headphone socket will I lose the microphone functionality as it seems to only has 1 plug?

Depends which model you have. The B750s comes in at least two variants, one with a volume control which has microphone funtionality, and one without, which doesn’t. If the plug on the end has 4 silver bands (3 dividing black bands) it will work, but if it only has three bands (2 black bands) it won’t.