People with unpaid tax on sold properties that are not their main homes are being urged to come forward and inform HM Revenue and Customs (HMRC) of their liabilities.

The move forms part of a new campaign to clamp down on such indiscretions, and a failure to come forward could result in a range of penalties, or even criminal prosecution.

The Property Sales Campaign is aimed at those selling residential properties in the UK or abroad, where Capital Gains Tax (CGT) should be paid on any profits made.

For example, this includes properties which people have sold that were given to them, as well as the sale of holiday homes.

Officials have said that people who come forward voluntarily will receive the best possible terms, as any penalty they pay will be lower than if HMRC comes to them first.

On the other hand, people who do not disclose details of what they owe will come under closer scrutiny.

"Some people will not understand that selling a second home, a holiday home or a property disposed of as a gift could attract Capital Gains Tax," said Marian Wilson, head of HMRC campaigns.

"Telling HMRC about your tax liabilities is simple and straightforward, and help, advice and support are available."

She added: "It is better to come to us before we come to you. After the opportunity closes, HMRC will use information it holds about property sales, in the UK and abroad, to identify people who have not paid what they owe. Penalties - or even criminal prosecution - could follow."

Through the new campaign, people have until August 9 to tell HMRC about any unpaid tax on property sales, and until September 6 to pay the tax owed.

After the date in September, HMRC will begin investigations into the tax affairs of those who have sold properties other than their main home, but who appear to have paid no CGT.

HMRC's website provides more details about the campaign, as well as offering help and support regarding the payment of CGT. People can also seek further guidance by calling HMRC directly on 0845 601 8819.