To add a little to the previos post.
For me an INTERCEPTING SEAR is a system where the tumbler has some type of projection which can be "caught" by a movable hook in the case of the main or trigger sear being accidently jarred and released say like when the hunter takes a fall or drops the rifle or whatever.
The "hook" remains in place ready to catch the tumbler regardless of whether the safety catch is on or off.
The hook is lifted clear by the first movement of the trigger pull during nomal operation/firing of the rifle.
Usually an intercepting sear is lifted clear of the tumbler to allow the tumbler to reach the striker by the trigger, NOT the safety catch.

On the other hand an INTERCEPTING SAFETY is a device which is placed in a position to deliberately block the fall of the tumbler/s in the event of the tumbler accidently falling.
This is like a solid block of steel which does not catch the tumbler but is standing solidly in the way.
This intercepting safety is removed from its position allowing the tumbler to fully impact the striker, by the first part of the trigger pull, or the safety catch being released, or sometimes by the top lever coming fully over as the gun is closed.

It's true though that in reality they are all a form of intercepting safety as they all "intercept" the tumbler fall in one way or another, and they all are an additional safety feature.

By the way, what does that extra screw shown in the Webley photo actually do.
I mean what lock internals require this extra screw?