The so-called Rigby-style fore-end latch was patented by Charles Harvey of Wilkinson's (later Wilkinson Sword) in 1866. It was much favoured and widely used by John Rigby (and Thomas Horsley, BTW) but not invented by him.

During the ‘Golden Years’ of double-gun development, there were some 29 patents for different fore-end fasteners registered in Britain alone! The three listed by Ed above are by far the most commonly encountered patterns.