Why was a British plan to rescue Dyer cancelled?

An SAS mission to rescue Edwin Dyer is reported in the Sun, of all places. They surely have this sort of plan in mind for every hostage situation, but it's unusual for them to talk to the media about it – a measure of their anger at the decision not to carry it out. Unfortunately it sits very uncomfortably with Jeremy Keenan's analysis. Thanks to Jim Mann Taylor at the 153 Club for circulating the Sun story.