"One thing we do know is that the decision was not taken by local commanders assessing their situation but by No.10. - Musket

This is a quote taken directly from his book "One Hundred Days", it appears on page 114:

"From CTG [Commander Task Group] 317.8, to "Conqueror", text priority flash - Attack Belgrano Group"

CTG and the author of "One Hundred Days" was Admiral Sandy Woodward - about the most senior local commander you could get down in the South Atlantic at that time. He sent that signal knowing full well it could not be acted upon as the three SSN's the UK had down in the South Atlantic were not part of his formation and were under the operational command of Northwood. But in sending that signal he knew damn well that it would succeed in doing the following:

1: Alert those back home of the severity of the situation

2: Let those back home know exactly what "their man in charge" on the ground wanted doing

The result was that the threat posed by the Belgrano and the Carrier Group to the North of the islands was recognised and Chris Wreford-Brown's Rules Of Engagement WERE changed to allow him to attack the Belgrano Group.

Here is something else Woodward says:

"My own case is simply stated, because it comes from the same folklore as that followed by Admiral Nelson, Admiral Jervis, Admiral Hood, Admiral Jellicoe and Admiral Cunningham. The speed and direction of an enemy ship can be irrelevant, because both can change quickly. What counts is his position, his capability and what I believe to be his intention"