Penal consequences

Assessee has collected service tax from clients but did not deposit it to govt. The default persists for over a year now..However, no SCN or any kind of Order/notice/ enquiry has been received from the department

Now the assessee wants to deposit the service tax so collected voluntarily, along with interest.

Will any penalty also be levied while making such voluntary payment..? Kindly explain the penal consequences, if any.