The House of Lords is so full-up that a cross-party group of peers and MPs have quietly set up a committee to look at how to cut its size.
There are currently more than 820 members in the House of Lords - up from 666 in 1999 - which makes the chamber second in numbers only to China's National People's Congress.
At present, there is not enough room to seat more than half the peers, which can lead to strict time limits on speeches during popular debates.
However, the number could be set to rise again as David Cameron is likely to appoint more Conservative peers to better reflect the make-up of the Commons.
The prime minister appointed 186 peers in his first term of office, compared with only 34 created by Gordon Brown in the preceding three years.
One MP who is involved in the committee said: “Either you’ve got to stop the number of peers coming into the Lords or you’ve got to start getting rid of some who are already there. It’s quite sensitive on how you would do this.”
The MP added that there was growing concern that an unelected chamber is being allowed to swell at the same time the number of MPs is set to shrink from 650 to 600 under proposals put forward by David Cameron.