In another TUPE case, the issue was about who does and who doesn’t transfer. In particular, is a long-term sick employee who isn’t working “assigned immediately before the transfer” so that their employment transfers under TUPE?
Agency workers have certain rights to equality of treatment at work. One of these is the right to be told about vacant positions that become available in the organisation they’re working in. It’s to give those temporary workers the same opportunity as direct workers to find permanent employment.