Advice please for possibly co-habiting

Hello mods,

I need a bit of advice re my partner potentially coming to share my 1 bed flat with me.

I am on DLA middle rate care and standard mobility. I get ESA Support Group both Contribution and Income related which obvs includes the SDP. I also get full housing benefit.

My partner (who would be moving boroughs) receives PIP Enhanced/enhanced, Support group, again both contribution and income related as well as housing benefit at his current address.

If I was to put him on my tenancy, would we continue to receive legacy benefits or would we need to make a joint claim for Universal Credit?

I know there are no premiums with UC and I expect that we would not qualify for transition payments because this is not classed as a natural migration? Am I right? I understand that transition payments are available for SDP claimants but am unsure as to whether we would qualify because we would be choosing a change in circumstances?

Finally, as I know and respect we would need to inform the DWP - would that mean we would both be reassessed for both ESA and PIP (or the UC equivalent of ESA Support Group)? I am worried that if we went on to UC we would have to start again with claiming LCWRAG?

Many thanks for all that you do,

Susie

PS I really apologize if you have already received this post - I am having a few tech issues!