Security threat level for London raised to 'severe'

[Casino67]

CNN.com:

London (CNN) -- New information has emerged from an intelligence operation about the possibility of an attack being planned in or near London, with subway stations and airports of particular concern to officials, a British security source told CNN Thursday.
CNN understands that the intelligence operation concerns a possible Mumbai-style attack, the source said.

The action is not connected to terrorism arrests last month in Stoke, Cardiff and London, the source said.

A second British security source said a decision was made Wednesday night to raise the terrorism threat level from "substantial" to "severe" for the civil aviation industry and London transport.

The overall, national terrorism threat level remains at "severe."
Increased security precautions have gone into effect at train and subway stations and Heathrow Airport, though an attack is not considered imminent, a second British security source said.

Britain's emergencies team, which is composed of senior politicians and police officials, met Thursday morning to discuss the situation, the second source added.

"The threat level to the UK is at severe, which means that an attack is highly likely, and has been since January 2010," said the Metropolitan Police in a statement.

[clearvision]

I'm confused... substantial to severe... would that be like yellow to orange or orange to red? How do they get buy using actual descriptive terms over there?