That frustration was reinforced by EU Commission President Jean-Claude Juncker, who also told EU legislators that "there is increasing urgency to negotiate this orderly withdrawal".
He observed: "As the clock counts down, with one year to go, it is now time to translate speeches into treaties; to turn commitments into agreements; broad suggestions and wishes on the future relationship to specific, workable solutions".
Michel Barnier said any attempt by Britain to gain a competitive edge through the use of what is termed "dumping" would jeopardize hopes the country has for a smooth and orderly withdrawal from the EU.
In a message to Mrs May ahead of next week's European Council summit, Juncker said the EU needed "more clarity on how the United Kingdom sees its future relationship".
Britain's government has said it does not want a customs union with the EU, without which the EU says it would need to regulate Northern Ireland's trade to avoid a return of customs checks.
Mr Juncker was cheered by Eurosceptic MEPs as he noted the UK's departure was due on March 29th, 2019.
"If nerve gas was actively used against civilians in one of our member states, I believe that the European Council should, in clear terms, express its full solidarity with the British people and the British government in addressing this issue", said Timmermans, who as Dutch foreign minister accused Russian Federation of downing an airliner flying from Amsterdam over Ukraine in 2014. "Now we have the chance to reduce the uncertainty for companies on both sides of the Channel", said he, without specifying what the extraordinary plans would be.
Britain has said it no longer wants to be part of the EU's seamless and tariff-free internal market and the customs union.
But he was heckled by one MEP who shouted "it is a British issue".
The bloc has repeatedly dismissed such an idea as "cherry-picking" and European Union chief Brexit negotiator Michel Barnier once again rejected on Tuesday.
The European Parliament's Brexit coordinator Guy Verhofstadt said talks he held with May and her Brexit minister David Davis last week had left him confident London would "see the advantages of such an approach".
"But you should not simply discard the idea of a customs union".