This section forms part of the set dealing with the functions of members of the Scottish Executive. Section 53 makes provision for the transfer of functions of a Minister of the Crown so far as they are exercisable within devolved competence so that they will be exercisable by the Scottish Ministers instead of by a Minister of the Crown.
The present section provides for some exceptions to this general rule where it makes sense for the function to continue to be exercisable within devolved competence by a Minister of the Crown as well as by Scottish Ministers. Section 57(1) provides for a further exception in respect of functions exercisable for the purposes set out in section 2(2) of the European Communities Act 1972. These functions are called “shared” or “concurrent” functions - see section 63(1). They are not exercisable jointly but they are exercisable separately by a Minister of the Crown and by the Scottish Ministers.
Where functions remain exercisable by a Minister of the Crown by virtue of this section, paragraph 6 of Schedule 4 prevents an Act of the Scottish Parliament from modifying (or conferring power to modify) any enactment so far as the enactment relates to powers exercisable by a Minister of the Crown by virtue of this section.  This does not, however, prevent the Scottish Parliament from repealing or amending the enactment so far as it relates to powers exercisable by the Scottish Ministers while leaving the powers exercisable by UK Ministers untouched.
Certain other functions which are executively devolved to the Scottish Ministers by an order under section 63 are similarly made exercisable by UK Ministers as well as by the Scottish Ministers.
The section also provides for certain non-statutory functions to be exercised jointly by a Minister of the Crown and the Scottish Ministers.
Commentary Part II: the Scottish Administration General