Campaigners for a second referendum are herding a flock of sheep down Whitehall to protest against the impact a no-deal Brexit could have on the farming community.

According to a new report commissioned by the supporters of second poll, more than half of UK farms could go out of business if Britain crashes out of the EU on 31 October.

Backed by the People’s Vote campaign and written by Dr Séan Rickard, former chief economist of the National Farmers’ Union, the report warns that 50% of farms could go under as the government would prioritise keeping down food prices for consumers ahead of protecting agricultural producers.

To coincide with the report and launch of the Farmers for a People’s Vote group, campaigners are taking a small flock of sheep past the Cabinet Office where no-deal planning is taking place.

The report says the EU and all the countries with whom it has free-trade agreements would immediately apply tariffs and non-tariff barriers on food imports from the UK in the event of a no-deal Brexit. At the same time, UK tariffs on imports would be slashed or reduced to nothing.

It argues: “The combination of the removal of support payments – only a proportion will be made up by enhanced environmental payments – and an adverse trading environment will render the majority of farm businesses unviable. By the mid-2020s a large proportion of farm businesses – 50% or more is not an unreasonable estimate – recognising that they face an unprofitable future will decide to cease trading.”

Farmers have warned the government that 40% tariffs on meat exported to the EU could lead to the mass slaughter of sheep.

Helen Roberts from the National Sheep Association in Wales said in July it would be “absolutely catastrophic” to leave with no deal and could lead to civil unrest among sheep farmers.

Rickard said:“The campaign to leave the EU was based on the idea that the UK would quickly secure a comprehensive new trading relationship with Europe and that leaving would have only positive impacts on UK farming. But today the reality looks very different.”

In the event of a no deal Brexit, Rickard argued that many industries would suffer but agriculture would feel the most serious economic shock.

“It is impossible to project the exact number of farmers who will go out of business”, he said. “What we do know is that over 40% of them will have no net income if the basic payment is removed. If at the same time the government removes all tariffs and so depresses prices, these two factors combined will render over 50% of farms in this country unviable.

“The possibility of any compensation from the government going anywhere near offsetting this is remote because so many promises have been made to so many other sectors and not all can be fulfilled.”

Guto Bebb, a Conservative MP campaigning for a second referendum, said he was very disappointed that Michael Gove, the former environment secretary, who understood the risks of no deal to agriculture, was now in charge of no-deal planning. He urged Conservative colleagues representing rural communities to consider their constituents and refuse to back a no-deal Brexit.

“Farming is at the very heart of what makes this country great – to put that all at risk for the sake of pursuing a disastrous no deal for which the public haven’t given their consent would be an outrage against democracy,” he said.

“I represent many farmers and agricultural workers in my constituency – they did not vote to put themselves out of work or to put their farms out of business, jeopardising their livelihoods. Many of them voted to leave the EU in good faith because people like Boris Johnson told them it would mean an improved trading relationship with the EU and a better future. The reality looks very different now.”