ACR ON DSCNT HAS TCASII RA TO STOP DSCNT.

Narrative

WHILE ON OUR DSCNT INTO LONDON GATWICK ARPT AND UNDER RADAR GUIDANCE BY APCH CTL RECEIVED CLRNC TO DSND TO 13 ZERO TO BE AT 13 ZERO BY SELSI INTXN. I STARTED MY DSCNT WHILE MY FO READ THE CLRNC BACK TO THE CTLR. AT 18500 FT OUR TCASII WAS ACTIVATED BY 'STOP DSCNT' 'STOP DSCNT.' AS I STOPPED THE DSCNT I AUTOMATICALLY STARTED CLBING AND WAS FORCED TO OVERSHOOT 19000 FT BY 400 FT IN ORDER TO SMOOTHLY PERFORM THE AVOIDANCE MANEUVER. ABOUT THE SAME TIME THAT OUR TCASII WAS ACTIVATED A FRANTIC SECOND VOICE TOLD US TO MAINTAIN 19 ZERO AND REPEATED THE CLRNC 3 OR 4 TIMES. THE WX WAS VFR AND WE SAW WHAT SEEMED TO BE A 320 AIR BUS APCHING AT OUR 11 O'CLOCK POS. DURING OUR DSCNT THE CTLR WAS GIVING ALMOST THE SAME INSTRUCTIONS/CLRNC TO ANOTHER ACFT WHICH I ASSUMED TO BE BEHIND US. I BELIEVE THE CTLR CONFUSED THE RADAR TARGETS AND GAVE US CLRNC TO DSND WHEN HE MEANT TO GIVE IT TO THE OTHER ACFT. ON LNDG I CONTACTED THE CTLR SUPVR AND HE INFORMED ME THAT THE SECOND VOICE WE HEARD WAS PROBABLY THE INSTRUCTOR CTLR WHEN HE REALIZED THE PREDICAMENT THE STUDENT CTLR PUT US IN.