As both Samsong7 and Panic Button have indicated, the vast majority of junctions which show a right filter light will only do so when oncoming traffic is halted. However, there are junctions where this is not the case. (There seem to only be a few of these junctions left but, at one time, they were quite common). The right filter only indicates that traffic is allowed to turn right, not that it has priority over any other traffic.
Accordingly, the driver who is travelling straight on has priority. (Unless he happens to have local knowledge, there's no reason for him to know that traffic approaching from the other direction, and turning right, can see a green filter light. Assuming that he sees a green light, he has every right to proceed normally across the junction without expecting traffic to turn across his path).
Chris