The government should pay sheep farmers to prevent the mass slaughter of lambs if there is no Brexit deal, union leaders have said.

Last year officials considered plans to cull animals that could not be sold but it is understood they are now considering monetary compensation instead.

The National Farmers Union president, Minette Batters, questioned what would happen to British produce if no deal is agreed that allows goods to be accepted.

“With 900 hours to go, it’s unacceptable for government to leave British businesses having to take this gamble,” she said.

Nick von Westenholz, the director of EU and international trade at the NFU, said sheep farmers were particularly vulnerable because they rely heavily on exports to the EU that could be halted for months if the UK crashes out of the bloc on 29 March.

“The negative impact on the sheep sector will be felt within weeks because of the time [of year],” he said.

The EU has said it could take up to six months to authorise imports from UK food producers. The NFU says this would be a de facto trade embargo, leaving sheep farmers with no option but to slaughter surplus animals.

While one MP joked in a meeting with NFU officials about holding a mass “Brexit barbecue”, the NFU said farmers would face a stark choice: kill their flocks or continue feeding them.

“If you had a surplus as a result of no deal, they would have to slaughter or feed them. It is possible we could have a ‘slaughter premium’ – a market top-up where the government would essentially be assisting the farmer,” Van Westenholz added.

Batters said no deal would “decimate” farmers, forcing them to rely on other parts of the world where they would face high tariffs for exports.

“In a few weeks, if there isn’t a deal with the EU, high export tariffs could effectively mean we have no market for four-and-a-half million lambs. A no-deal Brexit could decimate those farms up and down Britain, from our uplands to the Welsh mountains, to the rolling hills and the English lowlands,” she said.

Sheep farmers in Wales said on Wednesday it was “imperative” that were not left on the hook for government negotiations. The Farmers Union of Wales had meetings last week with the Welsh government and the environment minister George Eustice to discuss the “dire impacts of a hard Brexit on the sheep industry”.

The FUW’s director, Nick Fenwick, said: “Government actions – which have consistently ignored our warnings about ending up in precisely the situation we are now in – make it imperative that our industry be compensated.”

He said he welcomed the fact Eustice and the Welsh government were “considering the need to negate such an extreme situation” where farmers would be left with unwanted sheep.

On Tuesday, the environment secretary, Michael Gove, revealed that the government would apply tariffs to food imports in the event of a no-deal Brexit, to provide “specific and robust protections” to farmers.

He will also use quotas, possibly mirroring import levels, to guard against price shocks for consumers.

Although nothing has been confirmed, industry insiders believe this could involve large quotas for tariff-free beef and cheddar cheese to protect the frictionless flow of meat from countries such as Ireland, one of the largest exporters of these two goods.

White chicken meat from places such as Brazil and Thailand could also be given a zero tariff in the schedule expected to be published later this week because UK consumer demand for breast meat outstrips domestic supply.

But in areas where British producers are vulnerable, for example with lamb, low quotas and high tariffs could be set to stop cheaper cuts flooding the market from countries such as New Zealand.