R(H) 9/04 was a case where exacty this happened. The DWP awarded JSA to a man and woman on the basis that they were a couple, but this did not prevent the Council from deciding that they were not a couple for HB purposes. The (then) Commissioner commented:
“… that is not a desirable state of affairs. However, it is an inevitable possibility unless provision is made to make one decision maker’s decision binding on the other decision maker. That could be done, but has not been done as regards relationship issues”
