[dghf]

> Historically all the Peers could sit

Not quite. Scottish peers (to be precise, members of the Peerage of Scotland, which isn't quite the same thing) and Irish peers (again, more precisely, members of the Peerage of Ireland) elected representatives from their number to sit in the Lords, in much the same way as the hereditary peers do today.

Scottish peers got the universal right to sit in the Lords in 1963.

The right of Irish peers to sit in the Lords, if elected, survived Irish independence in 1922; however, the office tasked with overseeing their election, that of the Lord Chancellor of Ireland, was abolished with independence, so their numbers gradually dwindled: the last Irish peer to sit in the Lords died in 1961.