IIRC in the past the Tories had a Party Leader who was in the Lords and a PM who was in the Commons.
'Twas even worse
HH.
Lord Home (14th Earl of) became leader of the Tory party - and so PM - on 19th Oct '63, while still in the Upper House. On the 23rd Oct, he disclaimed (is that the right word?) his peerage and became Sir Alec (he was a KT) Douglas-Home.
He was elected MP on 12th November (for the [very] safe seat of Kinross and West Perthshire).
So - for 4 days we had a PM in the Lords.
For 20 days a PM who was in neither House.
Thereafter a PM who was an MP.