I was late making a payment for council tax. Almost without warning I received a notification of a summons at a court. To escape this I had to pay their costs of applying for a summons (about �25) and to pay the outstanding balance in full. If it had gone to court no doubt I would have been put on the defaulters register.
My advice if you have any outstanding bills put this to the top of the queue..they show no mercy!
Council's don't forward information to credit reference agencies, so late council tax payments don't directly affect your credit rating. Of course, if late payments result in a court judgement against you, this is likely to be noted by the credit agencies (Council records are confidential documents, so the agencies have no access to them. Court judgements are public documents, so they can affect your credit rating).
When I worked in Council Tax, I was always told that as it is all dealt with in Magistrates Courts rather than County Courts, then credit problems never come up. I don't know exactly how the credit agencies work in gathering info etc though.
We were also able to look at very bad payers' Experian files and I never saw anything about Council Tax on there, even the ones that had gone as far as committal to prison proceedings and had suspended sentences given.