From a UK ATC point of view, yes you can, RVR 800m is the cut off for Visual Approaches.
Confirm you can do a visual approach with 800m (~.5sm) visibility? That certainly is unexpected.
Here in the US, we need at least 3sm for a visual approach. A pilot can request a "contact approach" with at least 1sm visibility, although it is generally prohibited in airline (part 121) operations.