Nancy Pelosi has said there will be no chance of a US trade deal with the UK if the Good Friday Agreement is undermined by Brexit.

Speaking at the London School of Economics, the speaker of the US House of Representatives warned a future trading arrangement between the two countries is not guaranteed, and said it would not happen if the UK’s exit from the European Union violates the terms of the 1998 peace accord.

Ms Pelosi said: “First of all it is very hard to pass a trade bill in the Congress of the United States, so there’s no given anyway. But if there were any weakening of the Good Friday accords there would be no chance whatsoever, a non-starter for a US-UK trade agreement.

“The Good Friday accords ended 700 years of conflict. This is not a treaty only, it’s an ideal, it’s a value, it’s something that’s a model to the world, something that we all take pride in.

“It was a model and other people have used it as a model and we don’t want that model to be something that can be bargained away in another agreement.”

Britain Before Brexit: Northern Ireland Show all 12 1 /12 Britain Before Brexit: Northern Ireland Britain Before Brexit: Northern Ireland Derry, Londonderry A garage door displaying unionism, bolted shut, like a visual representation of Brexit Britain, locked to outsiders, safeguarding what’s inside Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Derry, Londonderry Rossville Street, the site of Bloody Sunday, where messages demand a severance with England. From this perspective, Britain is England in sheep’s clothing, the real empire, the centre of colonial power Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Bangor A political message in paint not yet dry, still forming, setting, adjusting, or in old paint finally eroding, melting away Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Bangor Moral judgement frames a residential view. The message seeks to make everybody involved in the religious narrative: those who don’t believe are those most in debt Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Castlerock The beach is sparse and almost empty, but covered in footprints. The shower is designed to wash off sand, and a mysterious border cuts a divide through the same sand Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Belfast Two attempts to affect and care for the body. One stimulated by vanity and social norms and narratives of beauty, the other by a need to keep warm in the winter night Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Belfast The gate to an unclaimed piece of land, where nothing is being built, where no project is in the making, where a sign demands the creation of something new Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Derry, Londonderry Under a motorway bridge a woman’s face stares, auburn and red-lipped, her skin tattooed with support for the IRA and a message of hostility to advocates of the Social Investment Fund Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Derry, Londonderry The Fountain Murals, where the curbs and the lampposts are painted the red, white, and blue of the Union Flag. A boy walks past in the same colours, fitting the scene, camouflaged Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Coleraine A public slandering by the football fields, for all to see or ignore. I wonder if it’s for the police or for the community Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Belfast A tattoo parlour, where the artist has downed tools, momentarily, bringing poise to the scene, which looks like a place of mourning, not a site of creation Richard Morgan/The Independent Britain Before Brexit: Northern Ireland Derry, Londonderry A barrier of grey protects the contents of this shop, guarding it from the streets outside, but it cannot conceal it completely, and the colours of lust and desire and temptation cut through Richard Morgan/The Independent

The US played an influential role in the Northern Ireland peace process, and former senator George Mitchell served as a peace envoy to the region for then-president Bill Clinton, eventually overseeing the signing of the agreement between the UK and Irish governments and all political parties in Northern Ireland.

Yesterday, the former prime ministers of the UK and Ireland, Tony Blair and Bertie Ahern, called for a second referendum on Brexit to protect the integrity of the Good Friday Agreement.

One of the most influential democrats in Washington, Ms Pelosi is currently on a visit to the UK and Ireland, and met with Labour leader Jeremy Corbyn on Sunday, when the pair discussed the need to protect the Good Friday Agreement.

Ms Pelosi is due to address the Irish parliament on Wednesday, and will meet with leaders from across the island during her visit.

A post-Brexit trade deal with the US has long been an aspiration of Brexiteers, and has been advocated by President Trump himself.

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The proposed deal has also proved controversial in the UK because of perceived lower standards of food and other goods from the US.