New claims for CTC

I have just tried to make a new claim for CTC for a cl who is eligible for the SDP.
The Gov website says that in order to make a new claim the cl must be getting the SDP or be eligible for it.

When I rang HMRC they said that the cl had to be in receipt of a benefit including the SDP and would not progress the claim.
In practice it wont matter as the SDP should be in place within the month to get backdating of CTC but I was wondering if anyone could point me at the legislation to say whether the person actually has to be getting the SDP or merely entitled to it

Reg 4A of the UC(TP) Regs -

No claim may be made for universal credit on or after 16thJanuary 2019 by a single claimant who, or joint claimants either of whom—

(a)is, or has been within the past month, entitled to an award of an existing benefit that includes a severe disability premium; and
(b)in a case where the award ended during that month, has continued to satisfy the conditions for eligibility for a severe disability premium.

Entitled I say :)

Thanks, I tried quoting this to them but they said that they have to have something from DWP to show the SDP applies. I was wondering whether there was any Tax Credits legislation (as opposed to UC legislation) that clarifies matters

Unfortunately, all relevant legislation (the No 21 Commencement Order and No 23 Commencement Order) simply refers to Reg 4A of the UC(TP) Regs.

From a practical point, HMRC are not equipped to work out hypothetical entitlement to DWP benefits. But in any case, you aren’t normally entitled if you haven’t successfully made a claim:
https://www.legislation.gov.uk/ukpga/1992/5/section/1/enacted