Take them off,you shouldn't crack the basin unless the spanner slips,you will need an old wood chisel to remove the mate,make sure you have a clean flat surface for your new taps and use plenty of silicone,have someone hold the tap firmly stopping it from turning while you loosen the nut,some old basins had square holes in them with a square flange on the tap,I've had this problem before and the base diameter of the new taps was smaller than the corner to corner measurement of the square,but you can get base plates to fit between the tap and basin,it is unlikely you will need them but hold the tap still anyway.
Rich
January 2010
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