As you said - it is at the polices' discretion - the same way a speeding offence might be ignored if taking a sick person to hospital - that still does not make it legal! Also if a cyclist is so worried about road conditions in a certain area why don't they just get off their bike and push it along the pavement until they feel safe to rejoin the road.
Sorry - but the law is clear - cycling on the pavement is an offence. If police do not enforce this under certain circumstances it still does not make it legal. If a cyclist runs into anyone whilst cycling on the pavement then they are at fault whatever the circumstances.