Feeling guilty about taking cash for a job – or maybe several – that you didn’t declare to HM Revenue & Customs? In the coming months you will be able to come clean as the tax man offers an amnesty.

If you have finished laughing, you might like to consider the last time HMRC offered an amnesty, in 2007, it spent £6million tracking down undeclared earnings and recovered £400million.

Then it approached just five banks for information about their customers. This time more than 200 banks, building societies and financial institutions are taking part.

If you have squirreled away any money that is not accounted for, even if you have used it to buy a house in Spain or a Hummer, watch out. “The risk for those with undeclared liabilities is high if they choose to ignore the amnesty,” says Phil Berwick, a Director in the tax disputes & investigation team at law firm McGrigors.

HMRC are not offering immunity from prosecution under what they call their New Disclosure Opportunity (NDO) and on any missing money disclosed above £1,000 there will be a penalty charged of 10% of the sum owed, although Phil Berwick warns: “A badly-managed disclosure under the NDO can lead to higher penalties or, potentially, prosecution.”

However, if you don’t take advantage of the NDO and you get caught the penalty could be between 30% and 100% of what you owe, not to mention the cost and time of an HMRC investigation. There’s also a greater chance of being prosecuted, with the hefty fines and possibility of imprisonment that that risks.

If you want to take advantage of the amnesty you have to notify the Revenue between

1 September and 30 November. After that it starts scrutinising the details from the banks.