CEST is fundamentally flawed because....
It wilfully ignores the relevant case law:-
Hall v Lorimer (Court of Appeal November 1993)
In arriving at the decision Mummery J said:
‘In order to decide whether a person carries on business on his own account it is necessary to consider many different aspects of that person’s work activity. This is not a mechanical exercise of running through items on a check list to see whether they are present in, or absent from, a given situation. The object of the exercise is to paint a picture from the accumulation of detail. The overall effect can only be appreciated by standing back from the detailed picture which has been painted, by viewing it from a distance and by making an informed, considered, qualitative appreciation of the whole. It is a matter of evaluation of the overall effect of the detail, which is not necessarily the same as the sum total of the individual details. Not all details are of equal weight or importance in any given situation. The details may also vary in importance from one situation to another.’
Its a 'qualitative' (as opposed to a 'quantitative') exercise so is probably very difficult (if not impossible) to capture in an algorithm. But in any case for HMRC its just window dressing. They just want everyone on PAYE.
(BTW I hate the new Reg design. I'm down from several visits daily to once a week.)