The frontrunner to lead Northern Ireland’s biggest political party has warned that the “stability” of the region’s power-sharing government will be at risk if the UK fails to take “decisive action” to overhaul problematic post-Brexit trading arrangements.

The warning by Sir Jeffrey Donaldson on Monday came as the veteran Westminster MP launched what is likely to be an unopposed bid to lead the Democratic Unionist party. His candidature follows a chaotic period of bitter infighting in the party, which led to last week’s resignation of Edwin Poots as leader just 21 days into his term.

Donaldson, who was narrowly defeated by Poots in May’s contest to replace Arlene Foster, is widely expected to be the only candidate this time around as party sources stressed the need to avoid another divisive contest so soon after the last one.

Donaldson said the DUP needed to unite “now more than ever in the face of the threats posed” by the Northern Ireland protocol, part of the 2019 treaty that secured Britain’s formal exit from the EU which imposes a post-Brexit customs border in the Irish Sea.

“If elected, I will ensure that the government doesn’t just listen, but recognises the need to take decisive action to deal quickly with the protocol,” Donaldson said on Monday evening. He warned that a “failure to act will undoubtedly have consequences for the stability of our political institutions and our economy.”

The protocol was a key factor in the ousting of Foster, as unionists revolted against both the principle of a trade barrier between Northern Ireland and the rest of the UK and the real-world impact. The requirements of the protocol could lead to shortages of vital medicines in the region and restrictions on importing products such as sausages and other chilled processed meats from the British mainland.

Donaldson did not however specify what action he wanted the UK government to take. But one DUP source said London could refuse to carry out checks on things like food destined for outlets, like supermarkets, in Northern Ireland and other goods not intended for export, since those goods would not find their way into the EU single market. The source acknowledged there would be “consequences” for the UK if it unilaterally took that action.

As the next DUP leader, Donaldson would be able to choose whether to continue a power-sharing government with nationalist Sinn Féin, or whether to pull out and force an early general election in the region, which is due to go to the polls next May.

During his brief tenure as leader, Poots had refused to collapse the institutions over the Northern Ireland protocol, outlining instead a four year plan to work against it.

Donaldson, who has represented Northern Ireland in the House of Commons for 24 years, made no reference to the issue that toppled Poots leadership — a side-deal struck between Sinn Féin and the Westminster government aimed at ensuring the nationalists did not walk away from the power-sharing deal.

The DUP’s MPs and Stormont representatives objected to the content of the deal — which proposed fast tracking legislation on the Irish language — and the principle of Westminster directly intervening in domestic Northern Ireland affairs.

Poots defied these objections and proceeded to nominate a new DUP first minister last Thursday, provoking outrage among his colleagues who forced him to resign.

“Unionism deserves better and Northern Ireland deserves better,” said Doug Beattie, leader of the more moderate Ulster Unionist party. Other politicians have criticised the DUP for putting politics ahead of pressing issues like healthcare, education and the economy.