Accessing cartridge on mixer tap

I have what I think is an older style Mondella/Watermark mixer tap that needs to have the cartridge replaced. I have changed cartridges on mixer taps many times before, but on this one, I can't find any screw that releases the end cap to access the cartridge. Any advice - other than replacing the entire tap - would be appreciated. I have attached photos of the tap, and the hole that is exposed - where I would expect to find the screw - after the handle is removed. It's a bit blurred, but there is no Allen, Philips, or flat balde screw in the bottom of the hole.