The Scots rarely threatened throughout the 80 minutes at Murrayfield and conceded five tries against their English opponents.
"It's hard to put into words what I feel," Bradley told Sky Sports News. "We knew the systems they would employ but my guys didn't play to our game plan.
"We've let everyone down. Today was completely unacceptable. We need to give a big performance next week."
Edinburgh have the chance to put right their heavy defeat when they travel to Munster next Sunday.