A British trawler has been seized by France and another has been fined, amid an escalating row over post-Brexit fishing rights.
French maritime minister Annick Girardin said the ships were cautioned during checks off Le Havre overnight.
She said the first did not comply right away and the second was not allowed to fish in French waters so was detained.
The environment secretary said he was "urgently" investigating the situation in relation to the detained vessel.
Responding to an Urgent Commons Question from the SNP, George Eustice said the detained vessel was on a list provided by the Marine Management Organisation (MMO) initially provided to the European Union.
He insisted the European Union did grant a licence to the vessel but it was "unclear" why, according to reports, it was subsequently withdrawn from the list.
Mr Eustice said he was awaiting further details from Marine Scotland and was expecting a response in the "next hour or so".
Deidre Brock, the SNP's environment spokesperson, said the captain of the vessel was due in court this morning after being arrested for fishing without a licence in French waters and it was not good enough that the environment secretary had so little information.
Ms Girardin said on Twitter one of the British trawlers was caught fishing in the Bay of Seine without the proper licences.
She said the boat was diverted to the port of Le Havre and detained by the judicial authority, where their catch could be confiscated and the boat held until a deposit is paid.
The boat's captain also risks penal sanctions.
The BBC has confirmed the boat being held is called the Cornelis Gert Jan, which operates mostly into and out of the port of Shoreham, in West Sussex, and is operated by MacDuff Shellfish of Scotland.
MacDuff Shellfish said its fishing activity was "entirely legal" and the vessel was "legally fishing for scallop" in French waters when it was detained.
The firm said it would defend itself against any claims and that its boat was just "another pawn" in the ongoing France-UK fishing row, urging UK ministers to "defend the rights of the UK fishing fleet".
Meanwhile, the other boat was fined for initially resisting the check, Ms Girardin added.
The minister said checks on the British vessels were standard during the scallop fishing season.
But she added they had also been undertaken against "the backdrop of the tightening of controls in the Channel, in the context of discussions on licenses with the United Kingdom and the European Commission".