Addressing Parliament's constitutional affairs committee on Wednesday, Guy Verhofstadt, Parliament's lead negotiator in the Brexit talks, also admitted there was a risk of a hard Brexit, which he said would be "bad for the EU but even worse for the UK."
The ALDE group leader also voiced concern about a recent "build-up of pressure" by both the EU and UK, a direct reference to comments last week by European Commission President Jean-Claude Juncker that the UK Brexit negotiators were "in another galaxy" compared with the EU.
He was responding to questions from some committee members who had expressed concerns about what was called the "rapidly deteriorating climate" between the two sides.
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Diane James, an independent member from the UK, described the climate in which the talks were taking place as "troubling" and accused the EU of employing "bullying" tactics in the early stages of the discussions.
Describing Juncker’s reported "galaxy" comments after a dinner with UK Prime Minister Theresa as "immature and puerile" James, formerly of Ukip, pressed Verhofstadt to urge a "toning down" in such rhetoric.
Another member, Polish ECR group MEP Michał Ujazdowski, also condemned Juncker, saying, "Telling people they are living in another galaxy does not improve the tone of the discussion."
Verhofstadt responded by saying, "As someone who has been involved in many difficult negotiations in my own country, what has happened over the last few days - and this build-up of pressure that we have seen recently - does not entirely surprise me.
"This situation will not change until 9 June after the UK general election, when the real negotiations will start."
His comments come on the same day Michel Barnier, the EU’s chief Brexit negotiator, was due to publish the EU’s negotiating directives, setting out in broad terms its demands in five key areas, including citizens’ rights and the divorce bill for Britain exiting the bloc.
The text holds few surprises after EU leaders already set out its political parameters at a summit on Saturday. It also covers just the first phase of the talks, on the terms of the UK’s exit from the bloc, with a second mandate, on post-Brexit UK-EU relations, to be agreed later. It will have to be rubber stamped by member states’ EU affairs ministers at a meeting on 22 May.
Barnier said, "It is an illusion that Brexit will have no material impact on people's lives and that a deal can be done quickly and painlessly."
Britain would need to put energy and effort into the negotiations and respect the financial engagements of its current membership in the EU - including existing debts - before talks about future ties can begin, he added.
Verhofstadt repeated the EU position that trade talks with the UK will not start until a financial settlement for its withdrawal from the EU has first been agreed.
On this, he told the committee, "It has been said that the financial settlement is about revenge or the UK being punished, but it is nothing to do with that.
"I have never been divorced but, in a divorce, there has to be a financial agreement between the two sides. That is only fair and it is the same with Brexit.
"You cannot ask the remaining 27 member states to pay the bill for a country departing the Union. This will not happen and I can tell you that none of the 27 are ready to do that."
He declined to be drawn on the size of any eventual settlement, saying, "It’s great for the media to produce figures but as far as I know no figure has ever been mentioned."
With concern in some quarters that the UK would prefer to keep the Brexit negotiations "behind closed doors", Verhofstadt called for "full transparency" in the discussions.
In a reference to the “negotiating directives” unveiled by Barnier on Wednesday, he told the packed committee, "With these, you will be able to see, read and feel the EU’s negotiating position on Brexit. I hope there is openness on both sides and no secrecy. Transparency in the talks will be very important."
Verhofstadt said his main priority was to ensure the rights and status of the three million EU citizens living in the UK and also British citizens living and working on mainland Europe.
On this, he made an impassioned plea for the "terrible uncertainty" facing affected citizens to be lifted "as soon as possible."
"Citizens have been facing this uncertainty for over a year, it affects thousands and thousands of people and it cannot go on. We are receiving thousands of emails from people asking us what will happen and whether we can help them.
"This situation is destroying lives and businesses and the first chapter to be negotiated must deal with this, as is stated in the negotiating directives outlined today by the Commission."
Further comment from committee member Jo Leinen, a German S&D group MEP, who said, "We cannot have a situation where a non EU member enjoys more benefits than a country that remains in the EU but my concern is that Britain will, as before, start to cherry pick the bits of the negotiations it wants and reject those it does not want."
His group colleague Richard Corbett was critical of the UK Tory government, saying the British public remained "blissfully unaware" of the UK’s Brexit negotiating stance.
He said, "People do not yet know what the government will be asking on a several fronts, such as UK participation in EU agencies and the customs union."