Debt counsellors don't have special powers, though they are taken a lot more seriously by creditors than individuals acting by themselves. If you want to, it is possible to make your own arrangements to try to freeze interest and make special repayment plans.
In general, the free help is usually a better idea. However, if you're keen to do it yourself, read the summary guide from Citizens Advice. Working through the techniques by yourself to see what's available is a useful guide, and should help you understand what the debt counsellors will do.
Here are a few tools to help you:
Debt Analyser. This quick tool from the Debt Advice Foundation helps you work out how much of your debts you can afford to pay back, for example, priorities like your mortgage or utilities and other creditors. It can then create a statement of affairs and individual creditor letters if you want to write to your lenders. The tool is best used in Excel (once saved to your computer), but there is an OpenOffice Calc version too.
StepChange Debt Charity has an online debt advice service which is available 24/7. If you get stuck, you can either live chat with an advisor or call them on 0800 138 1111 (8am to 8pm weekdays, 8am to 4pm Saturdays). The tool helps you decide what action to take about your debts, based on your individual circumstances. The service is completely free and anonymous, so is great if you want to ask a question in complete confidence.
StepChange also has several counsellors answering questions in the MSE Forum on any debt issue. You can ask an open question in the discussion thread or send a private question to one of the counsellors. You need to be registered on the forum to ask a question.