The British government has published its Brexit backstop proposals
The Brexit coordinator at the European Parliament has said a "backstop that is temporary is not a backstop".
Guy Verhofstadt was responding to UK government proposals on the backstop solution in the event of a no-deal Brexit.
The British government "expects" a backstop deal to the Irish border issue to end before 2022, after UK Prime Minister Theresa May acted to ease the concerns of her Leave-supporting ministers.
Mrs May appeared to have avoided a full-blown Brexit crisis and a cabinet resignation after a "constructive" discussion with David Davis on Thursday morning.
It followed speculation the UK's Brexit secretary was ready to quit the government over the details of the backstop proposal.
Mrs May also held separate face-to-face meetings with British Foreign Secretary Boris Johnson and International Trade Secretary Liam Fox.
The British government has published its proposal for a proposed backstop scenario to avoid a hard border here.
This will see the UK retain parts of the EU's customs union in the event of a wider UK-EU agreement finding no solution to the issue; but Brexiteers had become concerned as to whether the proposal would truly be "time-limited", as promised.
Following the talks between Mrs May and her top cabinet ministers, a paper outlining the plan provided detail of the time-limited nature of an agreement.
"During a temporary customs arrangement, the UK’s objective is to avoid a hard border between Northern Ireland and Ireland and maintain the status quo for traders in respect of customs processes. It is expected that the arrangement will also apply to the Crown Dependencies", the document states.
It adds: "The UK is clear that the temporary customs arrangement, should it be needed, should be time limited, and that it will be only in place until the future customs arrangement can be introduced.
"The UK is clear that the future customs arrangement needs to deliver on the commitments made in relation to Northern Ireland. The UK expects the future arrangement to be in place by the end of December 2021 at the latest.
"There are a range of options for how a time limit could be delivered, which the UK will propose and discuss with the EU."
However, Mr Verhofstadt was skeptical, tweeting that it was "Difficult to see how UK proposal on customs aspects of IE/NI backstop will deliver a workable solution to avoid a hard border & respect integrity of the SM/CU (Single Market/Customs Union).
"A backstop that is temporary is not a backstop, unless the definitive arrangement is the same as the backstop."
Difficult to see how UK proposal on customs aspects of IE/NI backstop will deliver a workable solution to avoid a hard border & respect integrity of the SM/CU. A backstop that is temporary is not a backstop, unless the definitive arrangement is the same as the backstop. #Brexit— Guy Verhofstadt (@guyverhofstadt) June 7, 2018
While the EU's chief Brexit negotiator, Michel Barnier, says they will examine the proposals under three questions.
These were whether it is a "workable solution" to avoiding a hard border; whether it respects the "integrity" of the EU's single market and customs union"; and whether it is an "all-weather backstop".
I welcome publication of #UK proposal on customs aspects of IE/NI backstop.— Michel Barnier (@MichelBarnier) June 7, 2018
We will examine it with 3 questions: is it a workable solution to avoid a hard border? Does it respect the integrity of the SM/CU? Is it an all-weather backstop?
The Tánaiste Simon Coveney has repeated that a legally-binding backstop is vital, and that a great deal of work "remains to be done".
"I look forward to discussing the UK's written proposals, aimed at making progress in the Brexit negotiations, with the Commission Task Force.
The task force will be assessing whether these proposals have the potential to help deliver the UK's repeated commitment to avoiding a hard border.
"Our strong preference remains an overall EU-UK future relationship which would resolve all issues.
"However, it remains vital that a legally-binding backstop is agreed to provide certainty that, in all circumstances, a hard border will be avoided.
"The EU has been clear that the backstop is an essential element of the EU-UK withdrawal agreement and that negotiations can only progress as long as all commitments undertaken so far are respected in full.
"Ireland and the commission have both stressed that substantial progress on the backstop is needed before the June European Council.
"Based on the negotiations between the UK and the Commission Taskforce in the coming days and weeks, Michel Barnier will make an assessment of progress, for consideration by the Taoiseach and his counterparts at the European Council three weeks from now.
"Clearly, a great deal of work remains to be done and this needs to be the highest priority for all sides in the weeks ahead."
Speaking earlier, Taoiseach Leo Varadkar said any backstop agreement cannot have a time limit.
He said: "I wouldn't say I'm confident at this stage... there have been a number of occasions now in the past weeks and months where there have been leaks or indications that a proposal was coming from London, and that proposal did not come.
"It's only when I see something in black and white, written down that I can comment on it in a meaningful way."
Additional reporting: Jack Quann