PEI_3721 - thank you. That was exactly the sort of stuff I was after. Our overriding authority is EU OPS, which says nothing really except giving basic definitions and that "appropriate performance data must be available".
Our company TALPA matrix for specially prepared runways only says that the measured friction must be downgraded one category and the performance done no that basis. Obviously if there are other contaminants on top, as we have no figures we are not legal to attempt a landing or takeoff, so need to wait for it all to be cleared.
The airport in question was Skellefteċ (ESNS) but I haven't found much in the Swedish AIP or AICs either.