MANCHESTER, England - Britain warned the European Union on Monday it would trigger safeguard measures in their divorce deal if the bloc failed to agree to changes to smooth trade with Northern Ireland, saying the agreement had "come apart even more quickly than we feared".

In the latest warning to the EU, Frost told the governing Conservative Party's conference he would present a new set of legal texts to support the government's earlier proposals for change to the so-called Northern Ireland protocol.

Frost did not say when the government would trigger what is known as Article 16 - allowing either side to take unilateral action if the protocol is deemed to have a negative impact - but media reported he could move by the end of next month. 

The EU has said the triggering of Article 16 would be "extremely unhelpful" and it will look at all options in response. 

"Without an agreed solution soon, we will need to act, using the Article 16 safeguard mechanism, to address the impact the protocol is having on Northern Ireland," Frost told a sparsely populated hall at the Conservative Party's annual conference in the northern English city of Manchester.

"That may in the end be the only way to protect our country - our people, our trade, our territorial integrity, the peace process, and the benefits of this great UK of which we are all part."

Since Britain left the EU's single market at the beginning of this year, difficulties in sending some goods from the mainland to its province of Northern Ireland has prompted the government to repeatedly call for changes to the protocol.

Those calls have been met by the EU repeatedly saying it would not renegotiate a deal that was signed by both sides in good faith and has urged Britain to find solutions rather than resort to threats.

Frost admitted the government had wanted to negotiate "something better" than the protocol, which created a de facto customs border between Britain and Northern Ireland, but would act independently to protect peace on the island of Ireland.

He blamed the EU's "heavy-handed actions" for threatening the delicate balance brought by the 1998 peace process that ended three decades of conflict between Irish Catholic nationalists and pro-British Protestant unionists.

"Yes, we agreed the protocol in that difficult autumn of 2019. We knew we were taking a risk -- but a worthy one," he said.

"And we worried right from the start that the protocol would not take the strain if not handled sensitively. As it has turned out -- we were right. The arrangements have begun to come apart even more quickly than we feared."

(Reporting by Kylie MacLellan and Elizabeth Piper; editing by Michael Holden/Guy Faulconbridge) ((elizabeth.piper@thomsonreuters.com; 07979746994; Reuters Messaging: elizabeth.piper.thomsonreuters.com@reuters.net))