The UK's Brexit secretary has denied that British Prime Minister Theresa May issued a threat that if Britain was not granted a preferential trade deal with the EU after Brexit, then the UK would withdraw its security co-operation.

David Davis said, however, that if there was no agreement at the end of the negotiations, then it would be bad for both sides.

Meanwhile, French President Francois Hollande has said the EU would first have to agree the terms of Britain's exit from the European Union, before the future trading relationship could be addressed.

There has been a considerable degree of unease about a key line in Mrs May's six-page letter triggering Article 50, delivered to the European Council president yesterday. 

Mrs May wrote: "in security terms a failure to reach agreement would mean our co-operation in the fight against crime and terrorism would be weakened."

In fact, Mrs May mentioned the word security four times, and she did not raise the concept of failure in relation to any other aspect of the talks.

Some have inferred that this was a threat by the British to withdraw its substantial military, security and intelligence assets from the European space if it does not get the trade terms it wants.

At a time when Europe is facing jihadist threats and more offensive posture from Russia, any such alleged threat is going down badly.

The European Parliament's interlocutor on the Brexit negotiations Guy Verhofstadt has said security was too far too important an issue to be bargained against an economic agreement.

Today, French president Francois Hollande said in Paris that the EU would first have to agree the terms of the divorce, before moving into the question of Britain's future trading relationship with the EU, effectively supporting the German chancellor's stance on the issue. 

Britain is desperate to do a trade deal within the two year term, but already there is formidable resistance to the idea.

Meanwhile, Taoiseach Enda Kenny called for the language of the Good Friday Agreement to be incorporated into the ground rules for the Brexit negotiations. 

Mr Kenny was speaking at the European People’s Party conference in Malta. He said the grouping had the leadership of the European Parliament, Council and Parliament as he appealed for their support.

The Taoiseach said the EU faced an unprecedented challenge that the architects of the EU had never envisaged.

Mr Kenny warned delegates of the dangers of the rise in populism.

He said that because mainstream politics had not been listening, good people had been pushed to the left in anger and to the right in fear.

Mr Davis earlier said that Britain hopes to address the issue of the border early in the Brexit process.

Mr Davis also said he does not expect Britain to have to pay £50bn (€58bn) to the European Union as part of the Brexit process.

He said the era of huge sums being paid to the EU was coming to an end.

British media reports have suggested that Britain could have to pay around £50-60bn in order to honour existing budget commitments as it negotiates its departure from the bloc.

"We haven't actually had any sort of submission to us from the Commission. But our view is very simple, we will meet our obligations, we are a law abiding country," Mr Davis told broadcaster ITV this morning.

"We'll meet our responsibilities but we're not expecting anything like that," he said.

"The era of huge sums being paid to the European Union is coming to an end, so once we're out, that's it."

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Britain's ambassador to Ireland has highlighted the importance of the trading relationship between the UK and Ireland, saying it means a free-trade agreement is particularly important to achieve. 

Speaking on RTÉ's Morning Ireland, Robin Barnett said the free-trade deal Britain is aiming for would be bold and ambitious and "greater than any before".

The ambassador said he does not think Britain's "special relationship" with Ireland will be affected as a result of the UK leaving the European Union.

"From our perspective it is clear that Ireland will be part of the EU negotiating team but also that we have some very special interests both east and west, north and south, particularly in relation to the Northern Ireland peace process.

"And I think our job here in Dublin is to work very hard to promote the bi-lateral relationship and also to ensure the shared concerns that the UK and Ireland have in relation to the future are protected during the course of the forthcoming negotiations."