A memo has been issued about how councils should handle new HB claims made by those with SDP following the new 'gateway' block on claiming UC.

https://www.gov.uk/government/public...-more-children

Paragraph 13 is the important one if you move to a new Local Authority and need to claim HB there. (My bolding)

13. Therefore, if a claimant moves to a new local authority (LA) area but they are in receipt of SDP with their HB this change of circumstance will no longer trigger natural migration to UC and they will remain on legacy benefits. From 16 January 2019 this would be a new HB claim as long as the claimant remains entitled to SDP. If the claimant is to remain on legacy benefits, then the transitional payment should not be made. This payment is to help claimant transition from legacy to UC, so would not be appropriate.
Para. 19 onwards about what should happen if you have SDP but mistakenly make a UC claim in error may also be of interest.