The U.K. government is seeking to phase in tariff cuts for agricultural products in its potential post-Brexit trade deal with Australia, according to a person familiar with the matter.

A lengthy transition period for liberalization would help protect British farmers, the person said, speaking on condition of anonymity. The transition period could be up to 15 years, the Sun newspaper reported on Friday.

The government has been divided over the terms of a trade accord with Australia, which is seen as a key post-Brexit prize by Prime Minister Boris Johnson. The U.K.’s National Farmers Union has strongly criticized the potential deal, warning of a flood of cheaper food imports which would hurt local farmers.

Read more: Johnson Leaves U.K. Door Open to Australian Tariff-Free Food

“Free trade deals present a fantastic opportunity for our farmers, for businesses of all kinds, for manufacturers,” Johnson told broadcasters on Friday. “It’s vital that as a great historic trading nation that grew to prosperity through free trade that we see these new openings not as threats but as opportunities.”

His official spokesman Max Blain told reporters earlier in the day that the government wants to make sure any deal will be in the interest of both consumers and business and won’t compromise animal welfare or food standards. The Department for International Trade declined to comment.

Britain and Australia agreed the bulk of a free-trade agreement in April and have indicated they want to conclude the pact by the G-7 summit in June. Australia Trade Minister Dan Tehan on Wednesday said the nations were making “good progress” in their FTA negotiations.

A deal between the U.K. and Australia is expected to increase Britain’s GDP by 0.02% over 15 years, according to a British government assessment.