In the US, OFAC has a variety of enforcement options available to it upon learning of a potential violation of US sanctions. In cases where OFAC determines that there is insufficient evidence of a violation, but that the activity in question could lead to a violation, OFAC may issue a Cautionary Letter. If OFAC determines that a violation has occurred but that a civil monetary penalty is not appropriate, OFAC may issue a Finding of Violation. OFAC may also impose a civil monetary penalty on determining that a violation has occurred. OFAC publishes guidance on a Finding of Violation, civil monetary penalties, and criminal prosecution, available here.
Finally, OFAC may refer the case to appropriate law enforcement if it determines that the activity warrants a criminal investigation and/or prosecution.
In the UK, the Policing and Crime Act 2017 added financial sanctions violations to the list of offenses eligible for deferred prosecution agreements (DPAs).
For more on potential outcomes of criminal enforcement in the US and UK, see here.