An excellent article in The Guardian, from the 1st March 2006:
When is a wholly unelected body actually more democratic than the elected alternative? When it's the House of Lords, says John Parkinson
Adolf Hitler won an election based on a clear policy programme, but that does not legitimise every action conducted under his rule. In a democracy it is right and proper that individual policy proposals be scrutinised, regardless of whether they were in the manifesto or no
That is one of the roles that the House of Lords should be playing in British democracy, and in many ways it performs it rather well. The point to emphasise is that it does so in large part because the majority of its members are appointed for life. Appointees are not dependent on parties for their future career.