HD, I take it all back. Apologies.
Did a bit of research and found this in MATS Pt 1.
It is CAA policy that Continuous Friction Measuring Equipment (CFME) should not be used on runways contaminated with wet snow, slush or water, and controllers must not pass runway co-efficient of friction measurements to pilots take in such conditions. The reason for this is that readings obtained from CFME equipment such as 'Griptester' and 'Mu-meter', unless used only on compacted snow and ice, are considered unreliable and in some cases may indicate a surface condition that is better than the actual condition. UK runways contaminated with compacted snow and ice are not normally made available for use, with Aerodrome Operators applying a 'back to blacktop' policy.
Only applies to UK, and went into the document in March 2011 - don't know if other countries have done the same. I know there has been work going on for many years to try and improve the information available to pilots on runway conditions, particularly in wintery weather. Previously I think the information was made available on request and accompanied by a warning about the reliability of the measurements. I can't help feeling this is a bit of a backward step. There's no question that a braking coefficient needs to be used in an informed and educated manner but to withhold information that could be of value if used correctly (to protect those who might use it incorrectly from themselves???) smacks of nanny State-ism!