Mono-block bath tap replace cartridge access

[Ulsinus]

I need to replace the cartridge of my bath tap but can't figure out how to access the cartridge.
The tap is about 20 years old and is not marked with a maker's name.
The basin however is marked with the maker's name Sottini. The tap was installed at the same time as the basin.
I've checked carefully and can't find evidence of a grub screw.

Grateful for the help and support of forum members

 

[cross thread]

Top dome probably screws off

 

[Ulsinus]

Thanks Cross Thread.
You were right.
Next step is to find a suitable socket.