Principal and principle
Principal is either a noun or an adjective, but both uses have very similar meaning. Principle is simply a noun.
Below is an extract from an excellent local government website promoting sustainable development:
Principal (noun): the most important person in an organisation.
e.g. "Mark was a great school principal: all the pupils and teachers adored him."
Principal (adjective): the first in importance, rank, value, etc.
e.g. "The crown jewels is the principal treasure in the Tower of London."
e.g. "The principal reason for the car crash was the driver falling asleep."
Principle (noun): a standard or a rule.
e.g. "As a matter of principle, Ursula refused to fly anywhere."
Cambridge City Council should have written:
"... committed to addressing the principles of sustainable development."
It is nevertheless a good thing that local councils have such principles: GCSE.com believes sustainable development to be very important too.