Created 06/02/2019
Important- From 16 January 2019, a new law prevents new claims for claimants entitled to the SDP at the time of claiming or at some time in the month before.  Legacy benefits would be claimed instead.  
'No claim may be made for universal credit on or after 16th January 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.”'
Housing Benefit guidance is useful to help understand this change.