A current sensor comprising a coil arrangement with three sense coil segments (7, 8, 9) connected to each other and arranged to be located in close proximity to a current conductor in an electricity meter so that a combined response of signals relative to the current in said current conductor from said sense coil segments is proportional to the rate of change of current in said current conductor, said sense coil segments: - being mounted in fixed relation in at least one direction to the current conductor, and each having a magnetic centre which is co-located with each other; and wherein a turns-area product of one of the sense coil segments is substantially equal to the sum of the turns-area product of the other two sense coil segments (7,9); said first sense coil segment acting in a first sense, said second sense coil segment having coil turns in the opposite sense thereby acting in a sense which is opposite to said first sense, and said third sense coil segment acting in the same sense as the first sense coil segment; such that the sensor has a null response to a current in at least one other current-carrying conductor in said electricity meter, such being located in a defined location relative to the coil arrangement, and - the sum of their turns-area products is substantially zero, taking into account the sense of the winding by the sign of the turns-area product, so that the coil arrangement is balanced and thus substantially insensitive to a uniform external AC magnetic field and to a first-order gradient AC magnetic field; wherein each of said three sense coil segments (7, 8, 9) have different turns-area products, said sense coil segments (7, 8, 9) are connected to each other in series, and each turn of the second sense coil segment encloses each turn of the first sense coil segment, and each turn of the third sense coil segment encloses each turn of both the first and second sense coil segments. - being mounted in fixed relation in at least one direction to the current conductor, and each having a magnetic centre which is co-located with each other; and wherein a turns-area product of one of the sense coil segments is substantially equal to the sum of the turns-area product of the other two sense coil segments (7,9); said first sense coil segment acting in a first sense, said second sense coil segment having coil turns in the opposite sense thereby acting in a sense which is opposite to said first sense, and said third sense coil segment acting in the same sense as the first sense coil segment; such that the sensor has a null response to a current in at least one other current-carrying conductor in said electricity meter, such being located in a defined location relative to the coil arrangement, and - the sum of their turns-area products is substantially zero, taking into account the sense of the winding by the sign of the turns-area product, so that the coil arrangement is balanced and thus substantially insensitive to a uniform external AC magnetic field and to a first-order gradient AC magnetic field; wherein each of said three sense coil segments (7, 8, 9) have different turns-area products, said sense coil segments (7, 8, 9) are connected to each other in series, and each turn of the second sense coil segment encloses each turn of the first sense coil segment, and each turn of the third sense coil segment encloses each turn of both the first and second sense coil segments.