Foreign secretary David Lammy has referred himself to the Environment Agency and could face a £2,500 fine after going fishing with JD Vance without the proper licence.
Lammy and the US vice president went carp fishing together during the latter's family summer holiday in the UK - although the adults did not manage to catch any fish.
JD Vance arrived in Scotland on Wednesday for the next leg of his holiday, but David Lammy could be forced to pay a fine of up to £2,500 after failing to obtain the appropriate permits for their fishing trip.
The Times reports neither Lammy nor Vance held a rod licence to fish, something that is required of anyone over the age of 13 in England and Wales before they are allowed to fish, even on private land.
Lammy has since purchased the necessary licence retrospectively and referred himself to the government's environmental watchdog.
The Foreign Office put the incident down to an "administrative oversight".
A spokesman said Lammy "wrote to the Environment Agency notifying them of the error, demonstrating how it would be rectified and thanking them for their work protecting Britain’s fisheries".
A Labour source told The Times there was "nothing fishy to see here".
US vice president Vance has mixed business with pleasure on the trip, indulging in a number of meetings with politicians, including having breakfast in the Cotswolds with Reform UK leader Nigel Farage on Wednesday.
Earlier this week it was reported Police Scotland was preparing for a "significant" security operation ahead of Vance travelling north of the border.
After arriving at Prestwick yesterday in Air Force Two, Vance and his family were driven to a short distance to a private country estate on the outskirts of Kilmarnock.