SCT controller described a pilot deviation event when an aircraft on an ILS RWY 8 to BUR turned off the approach; entered a higher MVA area and conflicted with traffic landing VNY.

Narrative

Weather was IMC throughout the area. Aircraft X was cleared for an ILS Runway 8 approach to BUR and communications transfered to the BUR tower approximately two miles outside of BUDDE outer marker. Aircraft X was then observed in a sharp left turn Northbound perpendicular to the Runway 8 final; still level at 3000 FT MSL. This put the aircraft into a 4000 FT MVA and approaching a 5000 FT MVA. It also put the Aircraft X in conflict with Aircraft Y making an instrument approach to the ILS Runway 16R at VNY. While I was attempting to communicate with Aircraft X; the FIMR controller; who had just de-combined positions; called over to BUR tower and relayed that Aircraft X climb to 5000 FT and put on a South heading to avoid further MVA and aircraft conflicts. Aircraft X then checked back on to my frequency; was asked what happened; and then re-sequenced back to an ILS Runway 8 to BUR. He was advised of a possible pilot deviation and asked to call the facility. Recommendation; this was obviously instrument training and the flight instructor certainly needs to stay aware of what the student is doing and take corrective actions. Since the flight was in IMC conditions; situational awareness is paramount.