Yes played 3 times with Curved Air: On January 29/30/31, 1972, so I don't think Yes canceled because of the support band,,,,,,
Is it possible that they had a tour contract with Jonathan Swift, and someone gave them a surprise bum deal. Or perhaps the intendant gave Swift the shaft? It would be interesting to know, because a Curved Air/Yes double billing would have been an interesting collaboration.
Yes playing on October 29 1971 would have drop KICKED Curved Air across the channel! PERIOD!
Curved Air was supposed to be the supporting act but later Yes refused to play with them in one show because they were afraid to be blown of the stage after Curved Air's second album release.