LONDON - Britain will tell the European Union again next week that "significant change" to the Northern Ireland protocol is vital for genuinely good relations between London and Brussels to be restored.

The protocol was part of the Brexit divorce settlement British Prime Minister Boris Johnson negotiated with the EU, but London has said it must be rewritten less than a year after taking force due to the barriers businesses face when importing British goods into the province.

European Commission Vice-President Maros Sefcovic, who oversees post-Brexit relations with Britain, said on Thursday the EU's executive would finalise measures next week aimed at resolving post-Brexit trading issues in Northern Ireland by the end of the year or early 2022.

But Sefcovic reiterated that he would not renegotiate the protocol, and that solutions would have to be found within the terms of a deal designed to keep an open border between Northern Ireland and EU-member Ireland.

Britain's Brexit Minister David Frost is due to give a speech to the diplomatic community in the Portuguese capital, Lisbon, on Tuesday.

He is expected to say endless negotiation is not an option and that London will need to act using the Article 16 safeguard mechanism if solutions cannot be agreed rapidly, according to extracts of his speech released by his office on Saturday.

Article 16 allows either side to take unilateral action if the protocol is deemed to have a negative impact.

"No one should be in any doubt about the seriousness of the situation ... The EU now needs to show ambition and willingness to tackle the fundamental issues at the heart of the Protocol head on," the speech transcript said.

"The UK-EU relationship is under strain, but it doesn't have to be this way. By putting the Protocol on a durable footing, we have the opportunity to move past the difficulties of the past year."

The European Commission's measures are expected to be presented on Wednesday.

(Reporting by James Davey Editing by Helen Popper) ((james.davey@thomsonreuters.com))