Police discovered fragments of text on Dart's laptop that revealed that the pair had used the computer to have a "silent conversation" to avoid possible surveillance bugs.
They would open a Word document and take it in turns to type, before deleting the text and mistakenly assumed that none of it would be stored on the machine.
However forensic experts were able to plough through 2,000 pages of computer code to decipher fragments of what was said.
These included Mahmood making a reference to Wootton Bassett and then adding "if it comes down to it it's that or even just to deal with a few MI5 MI6 heads".
More top news
Slightly cooler temperatures will replace the recent muggy weather while some areas will see heavy rain.
Andre Greipel won the final stage of the 2016 Tour de France as Chris Froome crossed the line arm-in-arm with his Team Sky team-mates
An attacker armed with a machete killed a woman and wounded two others in the southern German city of Reutlingen.