The EU will not be fixing complex trading rules that threaten all-island whiskey and dairy exports.

Ireland’s EU commissioner, Mairead McGuinness, told the Seanad’s Brexit committee yesterday that changing so-called ‘rules of origin’ requirements in the EU-UK trade deal, or in any other EU agreements, would be “problematic”.

“To be very clear, these rules of origin exist and are as they are,” she said. “Brexit is the problem. Brexit has caused so much disruption, including to this all-island dairy market, which has developed over time.”

She said that TDs and senators should continue to lobby the EU on the issues and that perhaps “in time we could look in a measured way at these issues”.

Dairy and alcohol producers on both sides of the border say the rules are leading to tariffs on Irish whiskey bottled in the North or Irish cheese containing Northern Irish milk, if those products are shipped outside the EU or UK.

William Lavelle, the head of the Irish Whiskey Association, told the Seanad’s Brexit committee on Monday that the Irish G  overnment needs to “push much harder” on the EU.

The European Commission has previously refused to change its rules to remove tariffs on UK flour containing foreign wheat, which is used by 90pc of Irish bakers.

The tariffs threaten to push up bread prices, but despite letters from the Tánaiste and minister for foreign affairs, the EU has refused to budge.

Dairy and whiskey producers want ‘mixed’ goods – those which cross the B order multiple times to be finished, bottled or processed – to be treated as EU goods in trade deals.

Over 10pc of Irish whiskey sold around the world last year contained components from distilleries on both sides of the B order, while up to four billion  litres of Irish and Northern Irish milk are  ‘mixed’ in to products such as butter, cheese or cream liqueur.

But Ms McGuinness said that traders should focus on resolving issues with the Northern Ireland protocol in the UK’s 2019 withdrawal deal.

“Changing those is problematic,” Ms McGuinness said. “What might be helpful is if we could get over these difficulties around the broader implementation [of the Brexit deal].”

She also complained about a lack of trust between the EU and UK since the British government unilaterally extended customs grace periods on food and parcel imports to Northern Ireland.

“If the UK were to take further unilateral action over the coming weeks, the EU would react firmly to ensure the UK abides by its obligations under international law,” she said on Tuesday.

“There comes a point in a relationship where, if you’re not being fairly treated or treated with respect, there is a need to respond.”

She repeated denials that the EU was considering imposing checks on Irish goods being exported to mainland Europe if the UK refused to comply with the protocol.

“There is no interest here at the Commission or in the EU to make the problem an Irish problem because clearly this is a Brexit problem.”