Farming leaders warned that a new free trade deal with Australia could leave livestock producers "struggling to compete" with cheap food imports.

As negotiations on the first major post-Brexit trade deal reach a critical stage, concerns have been raised that Australian producers could be offered zero-tariff access to UK markets - potentially opening the doors to a flood of beef and lamb imports produced to lower standards than required in the UK.

National Farmers' Union (NFU) president Minette Batters said that could cripple the competitiveness of the UK industry.

"We know that if we're to open up the opportunities of new markets overseas for UK farmers, we will have to offer greater access to our own markets in return," she said.

"However, this trade-off needs to be balanced, and we need to make sure concessions to our hugely valuable home market are not given away lightly.

"There is a very real risk that, if we get it wrong, UK farming will suffer irreversible damage rather than flourish in the way we all desire, to the detriment of our environment, our food security and our rural communities."

Tony Bambridge is Norfolk council delegate for the NFU and also keeps a herd of Lincoln Red cattle on the Blickling estate.

He said: "We are not against free trade - it is unfair trade where the issue comes.

"We are not against Australian farmers producing beef, but if they produce it by injecting animals with hormones which are banned in the UK, that is clearly an intolerable situation. The government has repeatedly promised it will not allow that.

"But it does worry me because Australia is a low-cost producer. There are lots of different things they do in their production system that we couldn't do in the UK, and they are operating at massive scale.

"Despite the fact they have got a significant distance to bring that meat, it would probably be price-competitive in the UK, so it could undermine our market.

"But, as I said, we are not against free trade. As long as it is produced to the same standards that we have to meet here, we have to try and meet that challenge."

The Financial Times reported a rift in the cabinet on the issue, with international trade secretary Liz Truss reportedly under pressure to grant tariff-free access for farmers in Australia and New Zealand in order to secure the new trade deals. However, environment secretary George Eustice is concerned that could spark a backlash from the UK farming industry.

While the Department for International Trade (DIT) would not be drawn on speculation, it said any deal signed with Australia would "include protections for the agricultural industry and will not undercut UK farmers or compromise our high standards".

Ms Truss, also the MP for South West Norfolk, added: "I am always looking to make sure, as I have committed to, that British farmers will not be undercut by unfair practices from elsewhere, and we will make sure in all the deals we do that British farming thrives. I am absolutely confident that will be achieved through the Australian deal."