Trade secretary Liz Truss has defended the "truly historic" new deal with Australia which opponents have branded a "betrayal of British farming".

The minister, also the MP for South West Norfolk, said the new free trade agreement "shows that global Britain is a force for free and fair trade around the world".

But East Anglia's farmers fear they could be unfairly undercut by cheaper food imports, produced to lower standards than are legal here.

Speaking in the Commons on Thursday, Ms Truss said: "I don't buy this defeatist narrative that British agriculture can't compete. We have a high quality, high value product which people want to buy, particularly in the growing middle classes of Asia."

She also told MPs they can "rest assured that this deal upholds our world class standards from food safety to animal welfare, to the environment".

"This deal with our great friend and ally Australia is just the start of our new post-Brexit trade agreements, and it's fundamental about what type of country we want Britain to be," she said.

"Do we want to be a country that embraces opportunity, looks to the future, believes its industries can compete and that its product is just what the world wants?

"Or do we accept the narrative some peddle that we need to stay hiding beyond the same protectionist walls that we had in the EU because we can't possibly compete and succeed?"

Many of the farming concerns relate to livestock and animal welfare, with organisations including the RSPCA and Red Tractor highlighting practises such as using growth hormones for beef cattle, hot branding and "mulesing" - the removal of strips of skin from the rear of a sheep to prevent parasitic infections. All are permitted in Australia, but banned in the UK

But there are also competitive concerns for East Anglia's sugar beet sector as import tariffs on Australian cane sugar are set to be eliminated in instalments, with a duty-free quota of 80,000 tonnes, rising to 220,000 tonnes after eight years - equivalent to 18pc of domestic production.

Kit Papworth, a director of farm contracting business LF Papworth based at Felmingham near North Walsham, is also a member of the National Farmers' Union's Sugar Board (NFU Sugar).

He said: "This [Australian] stuff is produced to totally different environmental standards than UK produce.

"The deal is an absolute dereliction of everything that farmers have been promised by successive agriculture ministers and the prime minister. It is farmers being sold down the river once again in a trade deal that will benefit other industries, while agriculture at the heart of the Norfolk economy is being left on the back burner to die.

"The real worry is this is the tip of a very bad iceberg, which will set a precedent for future agreements."

Gary Ford, East Anglia regional director for the NFU, called for more details on how the deal would safeguard the competitiveness of the region's farmers and ensure it will not "unfairly impact on our high animal welfare and production standards".

In the Commons, shadow environment minister Daniel Zeichner described the Australia trade deal as a "betrayal of British farming" and asked what measures will be put in place to help the sector.

Environment secretary George Eustice replied: "We've secured some important mitigations to help the farming industry including the fact that a tariff rate quota will remain in place for the first 10 years on both beef and sheep and for the subsequent five years there will be a special agricultural safeguard that means if volumes go above a certain trigger tariffs immediately snap back in.

"So we believe that we've put in place mitigations through that quota for the first 10 years and that safeguard."