The International Trade Secretary has “transferred” all enquiries about the plight facing firms to other departments, they say – despite it being her job to promote exports overseas.
A hard-hitting letter accuses Ms Truss of trying “shirk responsibility for the failures of your colleagues elsewhere in government”.
And it protests: “Most extraordinary of all, you are refusing to answer questions about the serious crisis affecting UK shellfish and fish exporters, and about the future of inward investment in Northern Ireland.
“At a time when British exporters are crying out for the government to acknowledge and address the problems they are facing in the wake of Brexit, the Secretary of State for International Trade cannot simply put their head in the sand and pretend that these issues are not their concern.”
Deliveries have been hit by the blizzard of new red tape, with requirements for health checks and customs documents – and ban on shellfish trade is “indefinite”, the EU is warning.
The UK is also locked in a bitter row with the EU over the harsh impact of Irish Sea trade checks, with the threat that the Northern Ireland protocol will unravel.
Labour, the Scottish National Party, the Liberal Democrats, the Liberal Democrats, Plaid Cymru, the Green Party and the Social Democratic and Labour Party, in Northern Ireland, have all signed the letter.
It says Ms Truss’s stance makes no sense because:
* The Department for International Trade (DIT) has responsibility “to promote UK exports and investment overseas.
“Are you really prepared to tell the UK fishing industry that you are only interested in the 30 per cent of their exports which go outside the EU?” it asks.
* DIT is currently offering “free advice” to exporters on “the practicalities of post-Brexit trade”.
* It is “not viable” to divorce trade with the rest of the world and with the EU – pointing to the wider impact of policy on food standards and data protection.
“There is no sensible, logical reason for you to refuse to answer questions about the UK’s trading relationships with the EU,” the letter states – accusing her of trying to “shirk responsibility”.
Ms Truss has been asked to respond to the criticism, ahead of trade questions in the Commons on 25 February.
A DIT Spokesperson said: “All parliamentary questions are directed to the department best placed to respond. This is standard practice in Governmentand has been the case under successive governments.
“The Cabinet Office lead the Brexit Business Taskforce to support businesses with regards to the EU Trade Deal.”