Cable may not need replacing just wait for the second electrician. I suspect the reading they have stated is a high earth fault loop impedance (Zs) due to a breakdown of conductor continuity, this is an assumption though. If this is the case it may be possible to correct this.Thank you for taking the time on a Sunday evening to assist me. If it is necessary I will instruct the replacement of this armoured cable although it will be a big job. Our safety is paramount of course.