Chris Paterson kicked four penalties and Dan Parks added another to hand Scotland their first win in this season's Six Nations Championship.
Jonny Wilkinson replied with three penalties as he became the leading points scorer in Test history - but England were otherwise unable to breach the courageous Scotland defence.
The success was eerily reminiscent of Scotland's win in 2006 when Hadden's men tackled everything in white which moved on the way to an 18-12 triumph, the points again supplied by the boots of Paterson and Parks.
This time, a 98% tackle completion was the key to Scotland's second successive Murrayfield victory over World Cup finalists England.
Hadden said: "Before we started the game, I was worried about how tentative and hesitant we looked - and perhaps that is not surprising, given the welter of criticism we have faced.
"It is not easy to retain your confidence when that level of negativity is aimed at you, but I continually told the players to never doubt themselves.
"In a nutshell, it was probably the defence of the first driving line-out where the players gathered their confidence. The way we defended that line-out and the one soon afterwards gave us the confidence to win the game."
Scotland were well-briefed on how to stop England.
"We knew it going to be tough up front, and it was a Herculean effort from our lighter pack to perform as they did - especially in the set-piece and also around the ruck area," Hadden added.
"We know we've got a good defence and we've been a little bit disappointed with how we have defended in the first three games.
"We've done a lot of uncharacteristically stupid things rather than missing tackles. But we felt the preparations had gone better this week, with more cohesion than we have had before - and that was certainly evident today."
Hadden spared words for the courage Rory Lamont showed in collecting a loose ball in his own 22, an action which led to him being caught flush in the face by Iain Balshaw's knee - before being carried off on a stretcher.
The former Edinburgh coach said: "Rory is still in hospital - but he's okay.
"It was a head knock, but he's stable - so we are monitoring his situation at the moment."