Bluebulb Projects' The Measure of Things presents:
510 is about four-fifths the number of Members of Parliament (The U.K.)
In other words, it's 0.780 times the count of Members of Parliament (The U.K.), and the count of Members of Parliament (The U.K.) is 1.30 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")