Conservative rebels have failed in their bid to guarantee standards for post-Brexit food imports as a major overhaul of farming policy cleared the Commons – despite some MPs accidentally voting the wrong way.

The Agriculture Bill represents the biggest change in farming policy for a generation as the nation leaves the EU and its Common Agricultural Policy (CAP), which has previously governed how the industry is regulated and funded.

During the bill’s report stage debate, senior Conservatives Simon Hoare and Neil Parish led the push for an amendment which would ensure a “level playing field” for farmers by guaranteeing that the UK’s high environmental, animal welfare and food safety standards would have to be met by any imported produce entering the country under post-Brexit trade deals.

The amendment was defeated by 277 votes to 328, although deputy speaker Dame Eleanor Laing said some MPs had mistakenly voted the wrong way via the new electronic system – but she added this would not have affected the result.

The division list showed 22 Conservative MPs supported the amendment, including chancellor Rishi Sunak – who made a mistake in the voting process rather than staging a shock rebellion against the government.

A source close to Mr Sunak blamed “online teething problems with the system”, adding: “The chancellor did not intentionally vote against the government. He called the chief whip straight away to explain.”

Before the debate, farming leaders in East Anglia had urged the region’s MPs to “speak up for farming” during the bill’s crucial report stage, but no Norfolk or Suffolk representatives joined the discussion.

Mr Hoare warned a change was required otherwise food imports to the UK would be “cheap for no other reason bar the fact that they were raised to lower standards”.

Mr Parish, chairman of the Environment, Food and Rural Affairs Committee, told MPs it was “time for us to stand and be counted” and support such measures.

He said: “I would say quite clearly to the secretary of state for trade (South West Norfolk MP Liz Truss) she should actually spend her time going out and dealing with a trade deal that has equivalence and makes sure we actually export our very important animal and environmental welfare.

“And I’d say to the Americans, why don’t you upgrade your production? Why don’t you reduce the density of population of your chicken? Why don’t you reduce the amount of antibiotics you’re using and then you can actually produce better chicken not only for America, it can also come into this country.

“Let’s not be frightened of putting clauses into this bill that protect us to have the great environment and welfare that the whole bill wants to have and farmers want to have.”

READ MORE: Coronavirus: Government urged to delay post-Brexit farm subsidy cuts by a yearBut environment minister Victoria Prentis warned of “unintended consequences” of amending the bill and insisted all EU import standards will be converted into domestic law by the end of the December 2020 transition period.

She told the Commons: “I’d like to reassure colleagues that all food coming into this country will be required to meet existing import requirements.

“At the end of the transition period, the Withdrawal Act will convert all EU standards into domestic law.

“This will include a ban on using artificial growth hormones in beef. Nothing apart from potable water may be used to clean chicken carcasses and any changes to these standards would have to come before this Parliament.

“We will be doing our own inspections to ensure that these import conditions are met.”

Ms Prentis said the government would consider calls for labels to be used to differentiate products that meet domestic production standards from those that do not.

For Labour, shadow environment secretary Luke Pollard said not including food standards in the bill could lead to a “race to the bottom”.

Conservative former trade secretary Liam Fox warned the US “would walk” in free trade talks if an amendment calling for food imports to match the UK’s “high standards” were to become law in the UK.

The bill later cleared the Commons after receiving a third reading by 360 votes to 211, majority 149.

It will undergo further scrutiny in the House of Lords at a later date.