Bit of an awkward one this.
MATS pt 1 appendix E under the standard phraseology for instrument approaches to landing there is:
"cleared visual approach runway (designator)"
Under phraseology for radar approaches there is:
"vectoring for (aid) approach; runway (designation)"
My interpretation that visual reference to the surface is an "aid" and therefore we can advise pilots that they ware being vectored for a visual approach to the runway in use.