Someone checked the rules at work yesterday. To form a quorum in the Lords requires just three peers, one of them acting as Speaker. They can vote, but just on general procedural matters. The Speaker can also vote, but it can't be the casting vote. This seems fairly pointless, as the only reason there would be a vote in the first place is that the other two couldn't agree, so every vote would look like this:

A quorum, yesterday
Contents: 1However—and this becomes a real issue in a senior debating chamber—nowhere does it say that that all the participants have to be awake.
Not Contents: 1

A quorum, yesterday