Hi Pace,
Does anyone know under what circumstances "Grand Father" allowances are given in respect to rule changes?
There is no legal principle of 'Grandfather rights'. It is an informal term, with no legal backing, used to describe a concession given to persons who may have practiced in some area of expertise or trade for a considerable length of time, but who are now faced with rule changes they could not have envisaged at the time they commenced to practice whichever skill or expertise is in question.
Now that is all that can be said about 'circumstances'.
However, the nature and extent of such rights is always decided on a strictly ad-hoc basis in relation to a specific situation.
However, if no 'grandfather rights' are given and the person affected is not consulted before the new rules come into force, and the rule change is likely to deprive him/her of his/her living, then he/she may perhaps have a line of action against the rule-makers on grounds of the common law principle of 'Natural Justice'.
Broomstick.