ACR WDB CLEARED TO CLIMB TO OCCUPIED ALT RESULTING IN LESS THAN STANDARD SEPARATION. OPERATIONAL ERROR.

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DURING CLBOUT FROM LONDON HEATHROW; CLRED DIRECT STU AND FL280; I REQUESTED FL310 (PASSING ABOUT FL267). WE WERE THEN CLRED FL310 AND I READ THAT BACK (INCLUDING OUR CALL SIGN). LATER PASSING FL286 WE WERE GIVEN AN IMMEDIATE VECTOR OF 190 DEGS AND TOLD OUR ALT CLRNC WAS ONLY FL280. DURING THE TURN (AND DSCNT) I SIGHTED TFC ABOVE AND TO THE RIGHT. LONDON CALLED THE DISTANCE ABOUT 3 MI. AFTER THAT WE WERE CLRED DIRECT SHANNON VORTAC (SNN) AND FL310. I DON'T KNOW HOW THE PROB AROSE; SO I CAN ONLY GUESS THAT IT WAS A MISTAKE TO GIVE US FL310 OR THERE WAS SOME COMS FAILURE/MISTAKE. THE AREA IS NEAR THE LONDON/SHANNON CTL BOUNDARY AND OPP DIRECTION TFC WAS INVOLVED. THE CAPT WAS RECEIVING AN OCEANIC CLRNC ON ANOTHER RADIO AT THE TIME; BUT I DON'T THINK THIS WAS A FACTOR. THE ACFT WAS ON AUTOPLT AND WORKLOAD WAS NORMAL. OUR FE HEARD MY READBACK OF THE CLRNC TO FL310 AND THERE WAS NO ADDITIONAL COMMENT FROM ATC. I HAVE JUST BEEN ADVISED VIA TELETYPE THAT ATC LONDON HAS ACCEPTED RESPONSIBILITY FOR THE TFC CONFLICT.