B727 CREW ON APCH INTO DEN BEHIND A B757 BELIEVE THEY WERE NOT PROVIDED PROPER SEPARATION BY THE CTLR.

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DUE TO ATC VECTORS; WE WERE PLACED AT 3 NM BEHIND A B757 ON FINAL (WE CALLED THE TFC IN SIGHT AND WERE CLRED THE VISUAL APCH) AND ALSO TOLD TO MAINTAIN 170 KTS. WE FEEL THIS PLACED US TOO CLOSE TO THE PRECEDING B757 AND SLOWED TO 140 KTS. WE TOLD ATC WE WERE SLOWING. THEY ASKED US IF WE COULD DO 150 KTS (NOW WE WERE JUST INSIDE 3 NM TO THE B757) AND WE SAID NEGATIVE. THE CTLR BROKE US OUT IN A R 360 DEG RACE TRACK PATTERN; THEN PROCEEDED TO JAM US BEHIND A BAE146 AT 3 MI AND TOLD US TO MAINTAIN 170 KTS TO THE MARKER AS WE WERE CO-SPD. HOWEVER; UPON SWITCHING TO TWR (AND OBSERVING TCASII); TWR INFORMED US WE HAD 60 KTS CLOSURE ON THE BAE146. WE IMMEDIATELY SLOWED AND CONFIGURED AND MAINTAINED SAFE SEPARATION FROM THE BAE146 (WE WERE CONCERNED; BUT NOT AS CONCERNED AS THAT AMOUNT OF SPACING FROM A B757 ON THE PREVIOUS APCH). WE FEEL WE WERE JAMMED INTO A LOSS OF SAFE SEPARATION (LESS THAN 4 NM) BEHIND THE B757 AND THEN GIVEN 'PUNISHMENT' VECTORS FOR NOT COMPLYING WITH THE SPD AND JAMMING US FURTHER; AND THEN BROUGHT AROUND AND JAMMED BEHIND THE BAE146 AND ERRONEOUSLY TOLD WE WERE CO-SPD; PRODUCING A HIGH CLOSURE RATE.