It was not proven to be *******s. There wasn't enough hard evidence to win a libel case. Those are two very, very different things.
Bob Maxwell won loads of libel cases. Presumably you think he was whiter than white, too?
The allegation was based on the testimony of a KGB colonel who had seen the KGB files on Foot and whose intelligence was impeccable in every single other regard. Why would he lie about Foot all of a sudden?