Benefit Cap exemption from PIP etc

Does anyone know where to find the answer to this possible idea?
Someone is affected by the Benefit Cap and at the same time applies for PIP (or any of the benefits that exempt a claim from the cap).
Eventually they are awarded PIP etc so are now exempt - from the date of PIP claim. Does that mean the cap reduction from the date of the PIP award should now be paid back to the claimant or will it only takes affect from the date of decision or even the date someone applies for exemption from the cap?

I think there’s wonderful potential for this, but only if the amount above the cap is repaid.
Can anyone help?

Cheers
Barbara

A15/2013 ( http://www.dwp.gov.uk/docs/a15-2013.pdf  )  suggests that that the LA should un-cap back to the award of the cap-exempting benefit and pay arrears : see para 41 (remove cap) and example 9.

The mechanism for this is slightly murky (to me) as there’s nothing specific on this aspect of the cap (ie re HB reg 75F - cap-exempting benefits) in the HB/CTB D&A regs 2001 ( http://www.dwp.gov.uk/docs/a8-2321.pdf ). Does the relevant benefit rule require the LA to go back to the award date ? (PIP is now a relevant benefit under s8(3)(baa) SSA 1998.)

Another scenario: Dla for a child stopped a few months ago. The benefit cap is applied, but the amount showing for CTC still includes the disabled child element. This will be stopped soon, with a probable overpayment. If the correct CTC is used, the reduction in HB will reduce considerably. The actual CTC payable is likely to be lower because of the overpayment - bringing the family income below the cap. So should the cap be worked out on the actual amount of CTC even though it’s wrong, or the actual entitlement. And what happens when the amount of CTC is reduced due to the overpayment?

NB DLA has been reapplied for and a DHP has been requested but I’m trying to work out the implications if DLA is refused.