There are a couple of things which might suggest that the peep is not original.

First, although the peep sight is quite well made, it just doesn't look like the quality workmanship you would expect from Holland.

Second, there is evidence that the rifle was at some time fitted with a cocking piece peep sight.
You can see the guide pin fitted in the rear bridge in one of the photos.

Maybe the cocking piece peep was original?

Whatever the case, the rear bridge peep should work really well in the field, that's for sure.