I have a small (approx 2.5" dia) device plumbed into the cold water supply
of a house I just bought. It is chrome in appearance, shape of a flying
saucer, and has the words "Water Governor Derve" on it.

I assume it is some form of Pressure limiting valve but I don't know. Every
time either the hot or cold water is turned on this device makes a
sqeaking/rubbing sound.

The cold pipe feeds a combi boiler and so I can believe it is a PRV to
protect the boiler input, but again, only guessing.

Can anyone shed any light on what the device is and where I could get a
replacement since I expect the noise is because it has worn, or is wearing,
out.

Thanks

Andy