I have clients who arrived in the UK 1998 claimed asylum at port and still await decision from HO. They have been receiving UCP/IS/HB until recently when their new IS96 arrived with a condition that they must sign every week at Croydon Reinforcement Unit. Also, the IS96 no longer has an expiry date. DWP have said they cannot accept this IS96 since the condition has been added. Is this correct?

Unless there's been a decision on the asylum claim I think they're wrong. So far as I can see only an asylum decision would bring the IS to an end. A change to their temporary admission conditions is not a decision on their asylum claim.