St. Margaret's church is on the grounds of the Houses of Parliament. It's one of the oldest churches in England, having been built by Edward the Confessor to accommodate the growing populace. The House of Commons and the Speaker have attended mass at St. Margaret's since 1614, and sermons were traditionally given by the Speaker's chaplain.
In 1643, early in the English Civil War, parliamentarian Edmund Waller plotted to return King Charles to London, an act of betrayal to the Long Parliament. Waller's Plot, as it was known - what an original name - was discovered by Long Parliament leader John Pym during a sermon at St. Margaret's. Pym immediately ordered the arrest of Waller and his co-conspirators from the church, and poor old Edmund was ultimately banished for his crimes.
I'm told the churchyard was a popular burial site for many centuries, but is a burial site ever really popular? I mean, they're not as good as nightclubs. Anyway, by the mid-nineteenth century, the yard became so overcrowded that doctors claimed the foul air would negatively affect proceedings in Parliament. The parish obtained a new burial yard on Fulham Road and relieved St. Margaret's yard of its many occupants.
Notable people to be married in St. Margaret's include the poets John Milton and Thomas Campbell, and diarist Samuel Pepys. Not to each other. To other people. I must make that clear.