(a) only one carer's allowance shall be payable to a carer, and only one carer's allowance shall be payable in any week in respect of the full-time care and attention being provided to a relevant person, and
(b) carer's allowance shall not be payable in respect of the full-time care and attention being provided to a relevant person in any case where a carer's benefit under Part 2 is being paid to any person in respect of the full-time care and attention being provided to the same relevant person.