The Welsh food and farming industry is in danger of “being put back decades” when the UK leaves the European Union, the environment secretary has warned.
Lesley Griffiths will meet Westminster counterpart Michael Gove for the first time since his appointment on the first day of the Royal Welsh Show on Monday.
She fears Wales will have less power and flexibility after Brexit if the UK government’s repeal bill becomes law.
Mr Gove said Welsh farming would have a new chance to “grow and flourish”.
First Minister Carwyn Jones and Welsh Secretary Alun Cairns are also expected to join tens of thousands of visitors on the opening day of the Royal Welsh in Llanelwedd, Powys.
Brexit is set to dominate the political agenda at the four-day event, Europe’s largest agricultural festival.
“I’m worried the Withdrawal Bill, coupled with the UK government’s lack of engagement with us to understand the needs of Welsh farmers, will mean this understanding is lost and the industry in Wales will move back decades,” said Ms Griffiths.
“Devolution has allowed us to tailor our policies for Welsh farmers with an understanding of their distinct needs.”
Concerns about the way the UK government plans to convert EU law into British law will be raised by Ms Griffiths with Mr Gove, whom she accused of showing “a complete disregard for devolution” after he postponed two planned meetings of UK agriculture and environment ministers.
The first minister also said he had not had a meeting with Mr Gove.
Speaking on Radio 4’s Today programme, Mr Jones added: “London shouldn’t become the new Brussels. We cannot have a Defra minister negotiating on behalf of Welsh farming without their consent.”
“We’ve offered a way forward, frameworks, rules. It has to be done by consent and not by imposition.”
The UK government’s proposed Withdrawal Bill suggests control over regulation being handed back from Brussels in these areas will temporarily be held by Westminster.
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UK government ministers say they need time to develop a legal framework for matters such as trade, animal health and farm subsidies that would apply UK-wide.
They insist it would include the flexibility for devolved governments in Wales, Scotland and Northern Ireland to make changes based on their own specific needs.
Plaid Cymru AM Simon Thomas, who will set out his party’s vision for agriculture post Brexit during a question and answer session at the Royal Welsh, said: “Plaid Cymru agrees with the need for UK frameworks as we leave the EU and wanted to work in building up those frameworks for agriculture, fisheries and for the environment,” he said.
“But the attitude of Tory ministers in Whitehall makes that impossible. What we are seeing now is not frameworks but impositions.”
Mr Gove, who on Friday announced farming subsidies would have to be earned rather than just handed out after Brexit, plans to “celebrate the success of the Welsh lamb industry” during his visit.
Global appetite is at an all-time high, he will say, with 40% of what is produced now exported around the world.
Lamb accounts for a third of Wales’ total food and drink exports – worth £110m last year.
However, 90% of what is sent overseas goes to EU countries.
Welsh farming unions and Meat Promotion Wales have insisted that ongoing tariff-free access to European markets is vital.
Ahead of his visit, Mr Gove said: “Leaving the EU will provide this hugely successful industry with new opportunities to grow and flourish and I am looking forward to meeting farmers and producers to hear their views on how we can drive the sector forward.”
Glyn Roberts, President of the Farmers’ Union of Wales said he had been “very disappointed” with the way Brexit discussions had been conducted so far and called on both the Welsh and UK governments to work together in a spirit of partnership.
He said the current situation was “laughable”.