Bluebulb Projects' The Measure of Things presents:
450 is about seven-tenths the number of Members of Parliament (The U.K.).
In other words, it's 0.69 times the count of Members of Parliament (The U.K.), and the count of Members of Parliament (The U.K.) is 1.4 times that amount.
(a.k.a. MPs) (2016 figures) (formally "Members of the House of Commons of the Parliament of the United Kingdom of Great Britain and Northern Ireland")
There are 650 Members of Parliament in the U.K. The Commons Chamber in the Palace of Westminster only has seating for 427 members, so those arriving late to House debates must stay standing.