Yes, it's VFR only. I'm not one for dragging pilots over the coals but if they took a chance and it wasn't VMC I'd have their licence. Clearance required also, although I don't think there is any problem with go arounds in VFR with mode C, the controller will need to be in control.
Those are great diagrams AlanM, thanks for taking the time to draw them. I think they bear out englishal's claim that there is no jet traffic at 1000ft just north and south of Heathrow. What is the minimum climb gradient you expect/require when departing?