A coreless current probe comprising a body defining an opening in a plane and a central line through said opening normal to said plane, whereby a conductor carrying a current to be measured can be accommodated in said opening so as to extend through said opening parallel to said central line; and characterized by: at least three coreless single point magnetic field sensors (20, 21, 22) distributed in said body around said opening with respective linear spacings between said sensors, at least one of said linear spacings being different from another of said linear spacings, said sensors each having a respective axis of magnetic field sensitivity (30, 31, 32) and being arranged in said body so that each of said axes is not co-planar with said central line; and sensing circuitry connected to said sensors which is operative to produce for each of said sensors a respective sensor signal which is a measure of the angle component of magnetic field at the sensor aligned with the respective axis of magnetic field sensitivity of the sensor, said sensors being arranged such that there are values of c r for which, in any homogeneous magnetic field, ∑ r = 1 n c r h r = 0, where n is the number of said magnetic field sensors, h r is said measure of said magnetic field component for the r th sensor, and c r is a constant factor for the r th sensor, said sensing circuitry being further operative to combine said measures h r employing the summation ∑ r = 1 n c r h r to produce a measured current value representing current following in a conductor accommodated in said opening in said body of said probe, where at least one value of c r in said summation differs from other values of c r, wherein: said sensing circuitry is adapted to derive as said measured current value the summation ∑ r = 1 n c r h r where the values of c r are selected to maximise rejection by the probe of external magnetic fields which are not produced by currents in a conductor engaged by the probe, and said values of c r are selected such that in any homogeneous magnetic field ∑ r = 1 n c r h r = 0. at least three coreless single point magnetic field sensors (20, 21, 22) distributed in said body around said opening with respective linear spacings between said sensors, at least one of said linear spacings being different from another of said linear spacings, said sensors each having a respective axis of magnetic field sensitivity (30, 31, 32) and being arranged in said body so that each of said axes is not co-planar with said central line; and sensing circuitry connected to said sensors which is operative to produce for each of said sensors a respective sensor signal which is a measure of the angle component of magnetic field at the sensor aligned with the respective axis of magnetic field sensitivity of the sensor, said sensors being arranged such that there are values of c r for which, in any homogeneous magnetic field, ∑ r = 1 n c r h r = 0, where n is the number of said magnetic field sensors, h r is said measure of said magnetic field component for the r th sensor, and c r is a constant factor for the r th sensor, said sensing circuitry being further operative to combine said measures h r employing the summation ∑ r = 1 n c r h r to produce a measured current value representing current following in a conductor accommodated in said opening in said body of said probe, where at least one value of c r in said summation differs from other values of c r, wherein: said sensing circuitry is adapted to derive as said measured current value the summation ∑ r = 1 n c r h r where the values of c r are selected to maximise rejection by the probe of external magnetic fields which are not produced by currents in a conductor engaged by the probe, and said values of c r are selected such that in any homogeneous magnetic field ∑ r = 1 n c r h r = 0. where n is the number of said magnetic field sensors, h r is said measure of said magnetic field component for the r th sensor, and c r is a constant factor for the r th sensor, said sensing circuitry being further operative to combine said measures h r employing the summation ∑ r = 1 n c r h r to produce a measured current value representing current following in a conductor accommodated in said opening in said body of said probe, where at least one value of c r in said summation differs from other values of c r, wherein: said sensing circuitry is adapted to derive as said measured current value the summation ∑ r = 1 n c r h r where the values of c r are selected to maximise rejection by the probe of external magnetic fields which are not produced by currents in a conductor engaged by the probe, and said values of c r are selected such that in any homogeneous magnetic field ∑ r = 1 n c r h r = 0.