But to install an iso the fuse would be required to be pulled. Certainly with in the midlands/east midlands, a 3P cutout especily M/C wont have the fuses pulled will be a cut outside on cable then reconnection. as far as im aware this is standard across all the DNO's in the uk now, was partly drawn up by HSE so is in most DNOs COP's. Any work carried out be it by the metering operator or the DNO will take into account the fact there is a M/C cutout, and will have it changed, the cost to be honest isnt that much for the DNO costs the same as fitting a one shot is most cases.