Stark warnings about the consequences of a no-deal Brexit have been outlined at a conference in Dundalk, featuring the three most senior civil servants in Ireland, Northern Ireland and Britain.

Martin Fraser, Secretary General to the Government; David Sterling, Head of Northern Ireland's Civil Service and Mark Sedwill, Cabinet Secretary in London, were guest speakers at the conference organised by the Centre for Cross Border Studies.

Mr Sterling said that for Northern Ireland the cumulative impact would be grave politically, economically and societally.

He said 35% of milk from Northern Ireland is sent over the border for processing and 44% of sheep are exported to the Republic for slaughter.

He warned of significant disruption to supplies, including foods, medicines and chemicals, leading to higher prices and also referred to the potential for civil unrest and public protests and disruption to normal life in the event of a no-deal Brexit.

Stressing the need for a return of the Northern Ireland Assembly, Mr Sterling said officials are no substitute for political leaders, adding that local ministers are needed back quickly and "we are the limit" of what civil servants can do.

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Mr Fraser told the conference of what had been achieved in terms of North-South and British-Irish co-operation in recent years.

He said North-South relationships have turned into friendships and "I think that's what is going to get us through the problems we are in at the moment".

He said there is no doubt the next few weeks are going to be crucial.

"We are all committed to protecting the Good Friday Agreement, Ireland's membership of the European Union, the Single Market and the Customs Union - that is absolutely fundamental for our economic future.

"We all want the same thing - I think now everybody wants the same thing… I think we have all looked hard at the what we have to do now is work our way through it, we have to protect all the gains, we have to rely on friendships and relationships and we have to find a way through."

He said ultimately the Good Friday Agreement is "about a way of life" that we have built in this country in the last 20 years "through agreement, by working together, through consent."

Mr Sedwill noted the meeting was taking place in Dundalk where during The Troubles, it would have been impossible to hold such a conference.

Mr Sedwill, a former UK ambassador to Afghanistan who has been Cabinet Secretary since June 2018, went on a tour of the border after his speech at today's event.

Speaking at the conference, he said the Good Friday Agreement had required political courage and painful compromises and we are in the home straight of a very challenging period as we seek to bring the Brexit process to a conclusion.

He said the UK recognises, as Prime Minister Boris Johnson said when he met the Taoiseach in Dublin recently, that leaving the EU was not a decision "our friends and partners in Ireland wanted" or expected.

He said the UK does recognise the consequences of the Brexit decision for the "economic and social connections across these islands" as well as "our responsibility in the UK to ensure that the underlying relationships and integration of our economies and societies is maintained".

Mr Sedwill said this is a critical moment in the history of Ireland and the UK, but said he is confident "we will navigate a way through it because it is so strongly in our interests that we do so".

He added that "we are doing so on the basis or relationships and trust and a common approach that simply didn't exist a generation ago in the same way."