What kind of Keyed entry door lock handle can I install?

I am currently one of 2 tenants living in a rented apartment in London. We have no locks on our doors and are looking to install Keyed entry door handles - however we have been told we are not allowed to drill new holes or damage any fixtures and fitting, and that the original door handles must be replaced at the end of our 2 year tenancy & fit. I have taken apart the door handle to see what we are working with and I found a most unusual situation in that the cross bore is quite different to what I am used to. It is not cylindrical instead with 1 hole and 2 lines going horizontally across which are 45mm in length end to end horizontally. The actual diameter of the cross bore is just under 1 inch in diameter. I am struggling to find any key locked door handles that would fit or replace this, please could you advise/ recommend ones? I have have photos of what I mean that I can provide, as well as a photo of the door handle for reference. Please advise as best you can. Thanks