40.—(1) Where, in relation to an award of an employment and support allowance, the Department makes a determination (including a determination made following a change of circumstances) whether a person—
(a)has or does not have limited capability for work; or
(b)is to be treated as having or not having limited capability for work,
which is embodied in or necessary to a decision under Chapter II of Part II of the 1998 Order (social security decisions and appeals) or on which such a decision is based, that determination is to be conclusive for the purposes of any further decision relating to such an allowance.
(2) Paragraph (1) applies to determinations made in relation to universal credit as it applies in the case of an employment and support allowance.
(3) Where, in relation to any purpose for which Part 1 of the 2007 Act (employment and support allowance) or Part 2 of the 2015 Order (universal credit) applies, a determination falls to be made as to whether a person—
(a)has, or is to be treated as, having or not having, limited capability for work; or
(b)is terminally ill,
that issue is to be determined by the Department, notwithstanding the fact that any other matter falls to be determined by another authority.