Beginning with A Stout Drainpipe:
From Oliver Goldsmith’s She Stoops to Conquer, a comedy first performed in London in 1773:
HARDCASTLE. Mr. Marlow—Mr. Hastings—gentlemen—pray be under no constraint in this house. This is Liberty-hall, gentlemen. You may do just as you please here.
A ‘pocket borough’ is a borough completely under the control of one person or interest. Pocket boroughs were so common that sometimes members of parliament were referred to as ‘Mr So-and-So elected on Lord This-and-That’s interest.’
In this affair, Dunny-on-the-Wold went from being a rotten borough to a pocket borough, under the control of Sir Walter. I am actually uncertain that even the death of all its voters would have been sufficient to end a rotten borough.
The 1832 Reform Act abolished 56 rotten and 130 pocket boroughs and added 41 boroughs to more equally represent population and industrial centres.