Britain needs to restore trust by fully implementing the protocol governing trade for Northern Ireland, European Commission Vice President Maros Sefcovic said on Friday
The official welcomed a British bid to co-operate with the EU on sausages.
Britain should show "unwavering commitment" to implementing the Northern Ireland protocol rather than "continually putting it into doubt", Mr Sefcovic said in a speech at the College of Europe, in Bruges, Belgium.
He said Britain should not make any further unilateral changes to the trading arrangements – as it did in March – and instead favour joint action through joint bodies.
"I welcome that the UK is recognising the value of this approach on one of the outstanding issues – the supply of chilled meats from Great Britain to Northern Ireland – because what the protocol truly embodies is trust," Mr Sefcovic said.
Britain asked the EU on Thursday for a further three months to resolve a dispute over whether chilled meat products, such as sausages, that are made in mainland Britain can be sold in Northern Ireland. The EU said it would consider the request.
The EU does not allow imports of chilled minced meat and "meat preparations", including sausages, from third countries – which Britain became after leaving the bloc.
Northern Ireland remains in the EU single market for goods, an arrangement designed to keep the Northern Ireland border with Ireland open and to maintain peace.
As such, sausage exports from Northern Ireland to the UK will be barred when a grace period expires at the end of June.
"Everyone around the table understood what this compromise meant in practice," Mr Sefcovic said.
"The EU will not and cannot accept this delicate balance being unilaterally changed or misapplied because of buyer's remorse."
Mr Sefcovic said the EU was willing to find creative solutions to the problem.
Britain's Brexit minister, David Frost, called Mr Sefcovic's speech "thoughtful and interesting" and said he looked forward to the EU's response to the British proposals.
"I agree, as he says, that there is still a 'window for productive political dialogue and positive results'," Mr Frost said on Twitter.
