I was working on a job the other day where an e.on man was fitting a smart meter.
In converstion he told me that e.on were taking out any flexible tails they found fitted between the cut out, meter and any isolator installed.
From the meter or isolator, the customers 'tails' if flexible would of course be left installed.
Seeing as how I'm trying to save more wear and tear on my digits which are now suffering badly after years of bending 25 & 35mm2 'tails' I'll keep using flexible 'tails' untiil I'm told oficially a reason not to.
Apparently this doesn't apply to various other service providers.