Many people wanted the number of MPs cut after the expenses scandal, it was part of the lib Dem 2010 manifesto to cut the number of MPs down to 500
It is bonkers for a third party to want to reduce the number of seats in a legislature. Of course, they didn't see their complete collapse in 2015. A 500 seat legislature could've given them as little as 1 seat maybe?
The Lib Dem manifesto in 2010 also included PR, which presumably went hand-in-hand with a reduction in seats. With PR, you could cut the number of seats down to 200 or so without losing anything of value, which ought to really be the populist argument in favor of PR.