In the "Rule, Britannia" department, Joan Collins relented Tuesday on her vow never to fly on British Airways when she caught a BA flight from London to New York. Last March, Collins vowed during a shouting match with an airline official that she would never fly British Airways again because the first-class seat she had reserved was unavailable and she was downgraded to coach class. Collins told reporters Tuesday she decided to fly British Airways because she prefers the speed of its exclusive supersonic Concorde flights. "I have a very forgiving nature," Collins said. "I don't think there is any point in bearing grudges about anything."