The European Union's chief negotiator on the Northern Ireland Protocol has said the UK must provide pathways to compliance with the protocol as soon as possible, and that trust was a "two way street."
European Commission Vice President Maroš Šefčovič also warned that if the UK did not take steps to implement the protocol, or to remedy measures taken through unilateral actions in March, the EU would "step up" legal action against the UK.
He told an event organised by the EU-UK Forum: "It cannot be just for the EU to seek solutions for practical problems that the UK flags up.
"The Withdrawal Agreement - including the protocol on Ireland and Northern Ireland - was agreed upon by the current UK Prime Minister and by David Frost, who was then the lead negotiator."
He added: "Likewise, trust is a two-way street. We have already shown - in the protocol - that we are willing to trust. Because for the first time the EU has entrusted the control of its economic border to an outside partner.
"But there is still a lack of implementation of these agreements by our partner, the UK, so we need to see pathways to compliance as soon as possible. We need to be able to trust the UK to live up to its international obligations."
Last week the EU agreed to extend the grace period allowing chilled meats from GB into Northern Ireland until 30 September.
Mr Šefčovič said he hoped this would provide stakeholders in Northern Ireland to adapt their supply chains in terms of sourcing such meats.
He repeated the EU's offer of a Swiss-style agreement on sanitary and phytosanitary (SPS) rules, which he said would do away with "the vast majority" of checks and controls on the Irish Sea.
He said a New Zealand-style equivalence agreement on agrifood standards, which the UK has sought, would not do away with all checks.
Mr Šefčovič told the forum: "In many of my contacts with stakeholders in Northern Ireland, I have had positive feedback to our idea of a veterinary agreement.
"I am well aware of the UK government’s initial concerns but remain optimistic that we can find a solution that works for everybody, most of all the people of Northern Ireland.
"We can also have a temporary agreement until the UK wants to opt for different SPS standards with another partner."