UUP leader Robin Swann has warned that Brexit cannot be exploited to help achieve a united Ireland.
He was speaking during his address at the UUP Spring party conference at the Slieve Donard Hotel in Newcastle, Co Down on Saturday.
The North Antrim MLA said that those who seek to exploit Brexit were acting selfishly.
"For those who think that they can exploit Brexit to pursue a united Ireland – you are not helping the people of Northern Ireland through such a selfish pursuit of your own agenda," he said.
"When Jim Nicholson and I met Michel Barnier and Guy Verhofstat last month our message was clear. Do not, no matter what others tell you, believe that all those Unionists who voted to remain in the EU, would vote to leave the United Kingdom in order to remain in the European Union; because they wouldn’t.
"My trip to Strasbourg was very useful. It told me that unionism needs to be doing more to ensure that our message is being communicated fully and effectively across the European Union. There has been no one as dogged as Jim Nicholson in making sure our message is heard loud and clear, and it is now time that everyone who cherishes the union joins him in amplifying it. There must be no doubt in the corridors of Brussels that Northern Ireland cannot be annexed from the rest of the United Kingdom.
Mr Swann called on the Irish government to work with the British government to get the best deal for Northern Ireland.
I have been clear that the outlined “backstop” is unacceptable to unionists. And if they are serious, it should also be unacceptable to those who say they want to defend the integrity of the Belfast Agreement throughout Brexit negotiations – because such an arrangement would totally undermine the principle of consent," he said.
If the Irish Government are serious about not harming the interests of the people of Northern Ireland, then it is up to them to work with – not against – the UK Government in finding solutions that ensure a frictionless border on the island after the United Kingdom exits the EU."
The UUP leader told the audience that he wanted to see more women and young people becoming involved with the UUP to reflect the diverse society currently living in Northern Ireland.
He said his party could continue to hold the DUP to account and resisted any talk of merging unionist parties.
"At our last Conference I spoke about the need for a new Unionism, and the need to promote the values and benefits of the Union. I still believe that we are the only Party that can reach out and win over converts, and convince others that our Union is a Union worth having," Mr Swann said.
"The union of the United Kingdom supports the rights of free expression, political freedom and the belief that we all have a role to play in building and sustaining civic society. We must make the case for self-assurance and greater confidence in our values and call for renewed efforts to maintain and grow the pro-union perspective that promotes a better and fairer understanding of how we make Northern Ireland work for all.
"I have often been asked why is there not just one unionist Party? Unionism needs the option of an alternative voice, because unionism is not a single homogenous grouping that fits neatly into a box and Unionism needs a conscience – and currently we are that conscience. Indeed, we have always been and will continue to be that conscience and that alternative voice.
"That ties in with my theme of radical moderates – it is up to us to say when others have gone too far or when others are abusing the positions they hold, or when others are being economical with the truth. It is a great responsibility to carry but it is one that this Party is well used to.
"We did so this week when members of the DUP were caught out retweeting anti-muslim tweets and when racist leaflets were distributed in East Belfast.
"Because neither I, nor this Party will stand by and allow unionism to become a byword for intolerance."
Mr Swann also addressed the Good Friday Agreement and the current political impasse at Stormont.
"Members – twenty years ago this Party took a significant step for the sake of people in Northern Ireland, in the Belfast Agreement, in our belief that things needed to change. For those of us who were around at that time, who may not have been on the same page then, I can assure you that I believe we are on the same page now. In holding a belief of what this Party stands for," he told the audience.
"Twenty years on we continue to respect and promote the values of reconciliation, tolerance, partnership, respect and mutual trust that our country needs to progress.
"This coming week we should be remembering our contribution to the Belfast Agreement, an Agreement that has been used as the foundation for peace deals in many other countries and conflicts around the world such as Sudan and Colombia, as a blueprint for how power sharing could work between two communities. We should also be recognising those individuals who took the risks for the greater good of our society, like our Party Chairman Lord Empey, David Trimble, Michael McGimpsey and many others.
"Sadly, the Belfast Agreement was not allowed to evolve and grow with society in the way it was envisaged because there were those who had much to fear from the normalisation of politics here. Twenty years on from 1998 there is little to celebrate when the DUP and Sinn Fein haven't been able to form a Government in the last 14 months, with one of them putting down a seemingly immovable red line of an Irish Language Act.
"Members, in 1998 the protections and support put in place in the Agreement for the Irish Language were meant to take politics out of the language – twenty years on we can see why that was the right approach.
"We are a devolutionist Party; we believe that the best delivery for the people of Northern Ireland is by the direction of locally elected Northern Ireland politicians. When the Assembly started to unravel, our party Chairman, Lord Empey warned others of how easy it was to walk down the steps, but not to under estimate how difficult it would be to get back up them. The current political impasse serves no one.
"In fact, the absence of a local Executive and Ministers is beginning to have a seriously damaging impact. Key decisions are going untaken, reforms are being delayed, money is being wasted, budgets are barely fit for purpose, major pieces of legislation are being steamrolled through Westminster and now civil servants are beginning to take major decisions in the total absence of any accountability."
The UUP leader ended his speech with a challenge to the party faithful.
"It is up to each and every one of us to carry the banner for this party, it is up to each of us to promote the Union and it is up to each of us to sell the message that this Party is the Party that is unashamedly, unapologetically and unrelentingly for the Union," he concluded.