Norfolk MP and international trade secretary Liz Truss insisted she would "never sign a trade deal that is bad for British farming" while launching a new campaign to boost food exports.

The government's Open Doors campaign, with the National Farmers' Union (NFU), Food and Drink Federation (FDF) and Agriculture and Horticulture Development Board, aims to target the growing middle classes in places such as Asia.

Speaking at the NFU's online annual conference, Ms Truss said the high quality of UK produce made it highly competitive and appealing to middle class consumers abroad.

But only a fifth of food manufacturers export their produce, she said.

The new £2m scheme will include advertising to encourage businesses to increase their overseas sales, practical "exporting masterclasses" and a new mentoring programme to help firms export.

The move comes in the wake of some UK producers struggling to export food products to Europe under the new post-Brexit regime.

There are also ongoing concerns, despite government reassurances, that trade deals with other countries could undermine high British standards and UK producers, who could be undercut by lower standard imports.

Quizzed about the threat to standards and farmers, Ms Truss said: "I want to be very clear, we are not going to lower our food standards in any future trade deals we sign, and I will never sign a deal that is bad for British farming.

"We are not going to lower our standards to secure a deal from the United States or any other trading partner."

She said there were huge opportunities to work with the US, for example, to end the ban on British lamb and to reduce whisky tariffs.

But she said: "In the same way we're not going to allow the EU to dictate our standards, we're not going to allow the US to dictate our standards either."

In her speech to the NFU conference announcing the new export campaign, Ms Truss said she wanted to "unleash the potential" of food and drink producers, and remove barriers to help them "get out into the global market".

Her speech came after prime minister Boris Johnson told the conference via a video message that he wanted people to buy more British food, and for more to be sold abroad.

"I'm delighted that already we've got back on the shelves around the world, we've got British beef back on American plates, pork trotters on Chinese tables and cheese on supermarket shelves across the Gulf," he said.