Any ATIS operates within the tolerances laid down as agreed by ICAO/The Met' Office/The CAA. These tolerances cannot be changed by ATC or the unit management unless new tolerances are issued by the above authorities.
We suffer from the same weather ambiguities as Cardiff as in that we are near the coast and susceptable to sudden changes in the weather.
Changes in wind direction or strength trigger a change in the atis, 1 knot won't do it, but 5 knots will, and I would have thought that this would be of interest to most pilots - if not, ignore at your own peril.