The Taxman is currently writing to taxpayers who are suspected of tax fraud, asking them to make a full disclosure of their wrong-doing under the contractual disclosure facility (CDF).
If you receive a letter offering the CDF, it is a very serious matter. The Taxman has taken a view that he could launch a criminal investigation into your tax affairs, but has decided that a criminal case is not cost-effective. Instead he is offering you a binding agreement to come clean, with the promise of low penalties.
You only have 60 days to decide whether to accept the CDF. If you don't reply in that period, the Taxman will start a formal investigation into your tax affairs, which could result in a criminal case. The CDF letter will also contain a denial letter, which you can sign and return if you believe you have no involvement in tax fraud.