I have just read an article written by a CAA IR examiner (in the current pplir.org magazine; the current edition is members only) which, if I read it correctly, says that the min vis can be 800m / 1.5 = 533m, with the right kind of runway lights, etc.
The minimum RVR required for single pilot ops is 800m unless a coupled autopilot is available. If met vis is reported you can factor it to get an RVR (if high intensity approach and runway lights are installed, x1.5 by day and x2.0 by night), but if an RVR below minima is reported you cannot factor this.