Liberal Democrat president Tim Farron has compared the legitimacy of the British Government to the brutal Syrian regime because of the unelected House of Lords.
Speaking on Sky News' Murnaghan programme, Mr Farron said it was not sustainable for half of Britain's Parliament to be appointed.
He was questioned about the allocation of 20 days of Parliamentary time to debating the issue in the coming months.
On the programme, Mr Farron followed Foreign Secretary William Hague who was quizzed about the situation in Syria and the Falklands.
Mr Farron said: "Isn't it ludicrous you were talking to William Hague about many undemocratic countries overseas and here we are and half of our legislature are being appointed and not democratically elected?
"I know it's not a sexy issue but it's unbelievably important if we are going to have a democracy that is even remotely modern.
"How can we have a Government that is even remotely legitimate, under whoever's banner it might be, if you've got half of our Parliament appointed, some of whom have inherited their places there?
"So, yes, it is very important. It won't be going on any of my leaflets because it's not really a top campaigning issue.
"But even though it is not, it is crucial to the future of our democracy and the Liberal Democrats are committed to making sure democracy is at least dragged into the 20th century."
Dermot Murnaghan suggested it was a "bit of a stretch" to compare the House of Lords with Middle Eastern regimes.
Mr Farron said: "If you have a government that is not elected that is a national embarrassment in one way and it is something we should all be concerned about."
Mr Farron said the Commons would need to spend less than 20 days on the issue of "dinosaurs" in both Houses if Parliament accepted the need to reform.