Green’s Dictionary of Slang

1. (Irish) an area of sanctuary in Dublin.

1828

High Life in London 3 Feb. 8/3: Langan is a native of Dublin, and was born in a place called from time immemorial ‘Mud Island’ [...] a kind of privileged fastness for rogues and robbers, and debtors and gamblers, &c.

2. Southend, the popular Cockney resort, which is sited at the seaward end of the Thames estuary.

1909

J. Ware Passing Eng. of the Victorian Era.