Sorry, I misunderstood your question.
CTS is quite a bit lower, although this varies by LA area.
The point I was initially making is that many people who were paying nothing / next to nothing pre 2012, are now paying full amounts.
Many have had real terms cuts in incomes, as you know from your extensive experience in the civil service. Plus,Council Tax rates have been rising higher than inflation for a decade or so.
Collection rates, to my knowledge, have decreased significantly. Unsurprising. Councils do take action via threats, debt collection agencies etc.. However, in most instances they are asking for money from people who often do not have a pot to piss in. Plus, councils are facing political pressure to tone down the use of court action and debt collection agencies. Many have set up emergency relief funds to assist those who have the least money.