Campaigns are schemes set up by HM Revenue & Customs (HMRC) to provide opportunities for you to voluntarily put your tax affairs in order.
Each campaign focuses on a different sector and if you intend taking part, you need to comply with the time limits for the relevant campaign. If you owe tax and don't come forward, it could cost you more if HMRC have to come to you.
If you are worried that you may not have declared some income or gains in the past, you may be eligible to disclose your affairs under a current campaign.