Almost £1.3 million in expenses and allowances was claimed last year by peers who failed to speak a single time in the chamber of the House of Lords, according to new research.
And 30 peers claimed more than £750,000 between them over the course of the last Parliament, from 2010 to 2015, without speaking once over the five-year period.
The chief executive of the Electoral Reform Society, Katie Ghose, denounced the figures as a "national scandal" which strengthened the case for reform of Parliament's upper house.
She called on Prime Minister David Cameron - who last month announced 45 new peers, bringing the total to over 800 - to take action to deliver a democratic second chamber
The ERS went through speaking and voting records for the Lords - not including brief interjections, written questions and answers or attendance in committees - to determine how many peers were failing to contribute to debates.
Peers are not paid for their work in the Lords, but can claim £300 a day for attending, whether they speak or not.
The ERS found a total of £1,262,670 was claimed in expenses and allowances last year by peers who did not speak. Some 55 of those who failed to speak in the last session also voted fewer than five times, but claimed £92,075 between them.
Eight who failed to either speak or vote in the last Parliamentary session (2014-2015) claimed a total of £29,812
And £772,719 was claimed by the 30 peers who failed to speak during the whole of the last Parliament.
Some 116 peers in total have failed to speak once since the start of the 2014 Parliamentary session, but have claimed £830,418 between them.
Ms Ghose said: "These figures show that the House of Lords is well and truly bust. That peers who failed to speak in the chamber during the whole of the last parliamentary session claimed three quarters of a million pounds in expenses and allowances is a damning indictment on the 'upper' chamber.
"Almost £100,000 of that was claimed by peers who voted fewer than five times, while just eight peers claimed £30,000 - despite not voting or speaking at all in the last session. This is a national scandal, and the sooner we sort out this mess the better."
She added: "The case is now stronger than ever for serious reform of Britain's unelected upper chamber - a chamber that is spiralling out of control, both in terms of size and cost.
"David Cameron announced 45 new peers at the end of August, swelling our already bloated upper chamber to over 800 members – an absolutely outrageous situation which will do nothing for people's faith in politics.
"The Prime Minister says he regrets not reforming the chamber in the last parliament. Given these new findings, now is the time to act on that and get on with the vital work of ensuring we have a democratic upper house, where the public finally get a say."