Abstract: Optical fibre interferometer for measuring a current carried by a high voltage line of the type comprising a winding traversed by a feedback current, having at least one base at earth potential, incorporating the interferometer core and the feedback winding, an insulating member and a measuring head mounted on a conductor traversed by the current to be measured. The insulating member is a rigid member forming a support or, in a preferred variant, a tubular insulating member having a flexible wall and provided with skirts made from an insulating material with a rounded "water droplet" profile.