They are the ghost army of Westminster:

Hundreds of ex-MPs with the right to haunt Parliament even though their Commons careers are over.

More than 350 former MPs – enough to form the largest party if they grouped together – hold coveted passes to the Palace of Westminster.

Reported by the Mail Online. You can read the full story here. 

I am a journalist and author. I am a staff writer at the UK edition of WIRED magazine and in 2015 my book, Freedom of Information: A Practical Guide for UK Journalists, was published. I created FOI Directory in 2012.