IT was always going to be a thorny issue during the run-up to Brexit, but now it appears the matter of the border between Northern Ireland and the Republic could dominate Brexit negotiations for months to come and could yet scupper any possibility of a trade deal.

In his strongest statement yet on the border issue, International Trade Secretary and arch-Brexiteer Liam Fox said yesterday that there could be no final decisions on the future of the Irish border until the UK and the EU have reached a trade agreement.

His comments came after the Irish Republic’s European Commissioner for Agriculture Phil Hogan said that the UK or at least Northern Ireland staying in the customs union would negate the need for a hard border, and added that Dublin could veto Brexit trade talks if the border issue was not resolved.

Hogan said it was a “very simple fact” that “if the UK or Northern Ireland remained in the EU customs union, or better still the single market, there would be no border issue”.

Fox’s statement contrasts directly with Hogan’s view and the official EU position that “sufficient progress” has to be made on the Irish border issue before negotiations on a future relationship – including the trade deal that is seen as vital to Scotland’s economy – can begin.

Theresa May’s position since her deal to form a government with the DUP has been that the whole of the UK will leave both the customs union and the single market when it leaves the EU in 2019, but she is known to oppose a “hard border” – with customs posts and possible passport checks – with the Republic.

In her speech in Florence in September May said that neither the UK nor the EU would accept any physical infrastructure at the border.

Arlene Foster, the leader of the DUP, then said she would not support “any suggestion that Northern Ireland, unlike the rest of the UK, will have to mirror European regulations”.

Fox told Sky News: “We don’t want there to be a hard border, but the UK is going to be leaving the customs union and the single market.

“We can’t come to a final answer to the Irish question until we get an idea of the end state. And until we get into discussions with the EU on the end state that will be very difficult – so the quicker we can do that the better, and we are still in a position where the EU doesn’t want to do that.”

LATER in that interview Fox accused the European Commission of having an “obsession” with ever-closer union between EU member states, which he said was delaying progress in Brexit talks.

Speaking after Fox’s interview was broadcast, shadow chancellor John McDonnell said he was “worried” by Fox’s comments.

He told Peston On Sunday: “I think the one thing that we don’t want to do is jeopardise any movement quickly, because we need movement to enable us to get into the proper trade negotiations. So I’m hoping that isn’t a Downing Street-sanctioned statement that’s he’s made.”

The EU has given the UK until December 4 to come up with further proposals on issues including the border, the Brexit divorce bill and citizens’ rights, if European leaders are to agree to moving on to trade talks.

The Irish Government has insisted on no hard border with Northern Ireland, with Taoiseach Leo Varadkar saying he must have written assurance from the UK before Brexit talks can progress.

In her speech in Florence this September, May restated that neither the UK nor EU would accept any physical infrastructure at the border.

Suggestions for alternate arrangements have included a new partnership that would “align” customs approaches between the UK and the EU, resulting in no customs border at all between the UK and Ireland.

Irish Foreign Minister Simon Coveney has said the UK’s desire for no hard border on the island of Ireland is “aspirational”.