Raleigh built the Quasar and Pulsar back in the 1980s, with oval tubing. A clubmate bought one of them that was built from 501 - I can't remember which model but I can remember that the back end flexed quite noticeably when sprinting or climbing out of the saddle.
EDIT - it must have been the Quasar that he had; I looked for a catalogue and found this one -
http://www.bulgier.net/pics/bike/Cat...4/ral84_07.jpg