UK authorities have seized shipments of tuna at UK ports as fears mount that illegally caught fish may be entering the supply chain.

The governmental Marine Management Organisation said it had identified potential problems with consignments of tuna caught by Ghanaian-flagged fishing vessels destined for the UK, and was holding them at ports while it investigated further.

“We are undertaking rigorous checks after issues were raised around the provenance of a quantity of tuna imported into the UK,” an MMO spokesman said.

The shipments were identified as UK authorities enhanced checks on imported tuna from West Africa in recent weeks to mitigate the risk of Illegal Unreported and Unregulated (IUU) fish entering the UK.

Defra wrote to seafood companies at the end of February, warning of “serious concerns about the contamination of the EU supply chain with IUU fisheries products”.

The letter outlined several issues including reliance on forged or fraudulent documents and unlicensed fishing. Goods could be suspended or placed under controlled movement orders at UK and EU borders until concerns were dealt with, it added.

The UK imports around 10% by value of its tuna from Ghana- worth about £27m annually [HMRC/MMO]. However, the UK’s biggest tuna brands said they had not, to date, experienced any disruption in supply as a result of the new regime.

MW Brands - which sources tuna off the coast of Ghana - said it was working with UK and EU authorities to enhance monitoring of tuna shipments. “These checks form a part of the standard ongoing verification process to which MW Brands fully adheres,” a spokeswoman said.

Princes said it had not identified any IUU fish going into its supply chain.

The warnings of a new EU-wide threat of illegal fish imports have already prompted other member states, including Spain, to reject a number of shipments because of concerns over their legality.