Transitional SDP element

I have a cl who is on CB ESA and is almost certain to get IR ESA, including the Enhanced DP and the SDP.
The cl is not getting anything for Housing Costs and his HB ceased for legitimate reasons some while ago. Those reasons no longer apply but to get Housing Costs he will have to claim UC.

If we apply for IR ESA but don’t wait until it is actually awarded can the transitional SDP be added to UC retrospectively or will they have to wait until they are actually paid the SDP before applying for UC?

Logic tells me that this should be OK, the UC decision was made in ignorance of a material fact (the award of SDP) so should be revised but I am looking for anyone’s experiences of actually doing this and what (if any) hurdles were put in the way.

Just a small point: a UC decision can only be revised on the grounds of ignorance of a fact if the result is to award less UC than in the original decision.

What you want is D&A Reg 12: revision when there is an increase in the rate of another benefit for a period that includes the date of the original UC decision (which it does because of the 2w ESA(ir) run-on).  This is an “any-time” ground for revision so it doesn’t matter how long it takes to sort out the ESA.

Or even Art 24 of the No 9 Commencement Order…