Why no referendum on Council tax increase?

In 2010 the coalition government said any council tax increase over 2% would need to hold a referendum to implement such an increase. This has been modified so Councils in the bottom quarter of the list of Councils can increase by £5 or 2% whichever is greater. SCDC has decided to increase by £5. That is a 3.84% increase in their portion of the council tax.