EU citizens in Britain are the victims of “political games” and their rights must be the first item in the exit talks, the European Parliament's chief Brexit negotiator has said.

Guy Verhofstadt called for the fate of those three million EU nationals, and of British ex-pats, to be settled before negotiations on the rumoured £50bn “divorce bill” – long thought to be the key early dispute.

Mr Verhofstadt said the EU parliament would agree a resolution soon after the Article 50 exit clause is triggered in the next few weeks, which it would expect to guide those talks.

Otherwise the parliament could exercise its right to vote down any eventual deal agreed between the UK and the European Commission. “We vote no – that is possible,” he told BBC Radio 4.

Mr Verhofstadt also ridiculed Theresa May’s hopes of concluding a new trade agreement before Brexit is completed in 2019, saying: “Let’s not be naïve, it will not take two years.

“In total, it will take two years plus the whole period of the transition to sort out this new partnership between the UK and the European Union.”

On Monday, MPs are expected to overturn a Lords amendment to the Brexit Bill demanding the Prime Minister give a unilateral guarantee that EU citizens will be able to stay in Britain.

The European Parliament’s backing for that controversy to begin the exit talks would be a boost for Ms May’s determination for EU leaders to act simultaneously.

Mr Verhofstadt said: “The first thing to do – in my opinion, maybe the most important – is to be aware of the difficult position of the EU citizens living in Britain and the opposite, the UK citizens living on the continent.

“It is absolutely necessary that, before talking about everything else, we need to clarify that UK citizens and European citizens cannot be the victim of the political games we have seen since Brexit.

“In my opinion, we need to put first in these negotiations the treatment of these EU citizens living in Britain and of UK citizens.

“This is the first chapter of the withdrawal agreement – then there can be, for example, the whole question of the money.”

The Parliament’s resolution would also emphasise the need to ensure 20 years of peace in Northern Ireland was not thrust into jeopardy, he said.

“No hard border. We cannot return to a hard border ... that is not in the interests of anybody,” Mr Verhofstadt said.

And he repeated his call for the Brexit negotiators to listen to the requests he has received from thousands of Britons anxious to remain EU citizens after withdrawal is completed.

“All British citizens today have also EU citizenship. That means a number of things: the possibility to participate in the European elections, the freedom of travel without problem inside the union.

“We need to have an arrangement in which this arrangement can continue for those citizens who on an individual basis are requesting it.”