To view the updated guidance on how to make a voluntary disclosure, follow this link to the HMRC website: https://www.gov.uk/government/publications/hmrc-your-guide-to-making-a-disclosure/your-guide-to-making-a-disclosure
HMRC customer helpline details:
Telephone
0300 123 1078
Outside the UK
+44 300 123 1078
Opening Times
Monday to Thursday, 8:30am to 5:00pm
Friday 8:30am to 4:30pm