This is a Deeley and Edge action. also known as the Westley-Richards Sliding-Block Rifle. This action is discussed in The Gun And Its Development by WW Greener, p.715. Here is the entire text:
"The Westley-Richards Sliding-Block Rifle
This breech-action, the joint production of Messrs. Deeley and Edge, has been, and is, extensively used in match rifles, for which type of arm it is well suited, although originally intended for a military weapon.
The mechanism consists of a vertically-sliding breech-block, which contains the tumbler, main-spring, and other lock work. The guard and lever are in one, and are pivoted to the body of the action, beneath the barrel. By depressing the guard the breech-block descends, as in the Henry carbine, the hammer - or rather tumbler - cocked, and the cartridge extracted.
It possesses a signal advantage over the Martini and Swinburn by allowing the barrel to be cleaned from the breech - certainly always a convenience, and a desideratum in match rifles."
