Required separation must still be maintained. You're only doing a visual approach, you haven't cancelled IFR.
So - separation is applied. In non-radar environment that's achieved either visually (as you summised) or by laid down (unit specific) geographic separation.
MATS pt.1 lays down reduced separation in the vicinity of the aerodrome. (section 1, part 3)
3 Reduced Separation
3.1 In addition to the following paragraphs, standard separation may be reduced when
authorised by the CAA and published in MATS Part 2.
3.2 In the Vicinity of Aerodromes
In the vicinity of aerodromes, the standard separation minima may be reduced if:
a) adequate separation can be provided by the aerodrome controller when each
aircraft is continuously visible to this controller; or
b) each aircraft is continuously visible to the pilots of other aircraft concerned, and the
pilots report that they can maintain their own separation; or
c) when one aircraft is following another the pilot of the succeeding aircraft reports
that he has the other in sight and can maintain separation.
Hope this explains