Britain should start talking about rejoining the EU, according to a former senior civil servant who ran the Brexit department.

Philip Rycroft, who was permanent secretary of the Department for Exiting the EU, said the “argument was there to be won” about going back into Europe, adding that a “clear-headed appraisal of what is in the country’s best interests” was needed. However, he said rejoining the bloc could be a “long and windy” road.

“Most economic analysis suggests that we have taken a significant hit to GDP as a result of leaving the single market,” he wrote in the Times. “The precise number, and the impact on our export performance to the EU and beyond, might be subject to debate, but no one can credibly claim that we have marched to the sunny uplands of sustained economic growth as a consequence of Brexit.”

Rycroft said the promises of the Brexit campaign on issues from economics to immigration had not lived up to expectations. “The great promise of a comprehensive trade deal with the USA now seems like an impossible dream,” he said.

“Chill winds don’t just blow through the international trading order. The postwar certainties that underpinned our security as a nation are visibly crumbling. With a hot war on the European mainland perpetrated by a revanchist Russia and an increasingly disengaged America, it is beyond peradventure that we must look to solidarity with our friends and neighbours in Europe to secure our defences.”

He concluded: “The argument is there to be won. It is time to talk about rejoining. It might be time to knock on the EU’s door.”

Rycroft’s comments chime with a growing mood within Labour that the party should be bolder on getting closer to the EU or rejoining in future. A number of cabinet ministers want Keir Starmer to push harder on trying to join a customs union or the single market, which are still red lines for the government as it seeks a stronger post-Brexit relationship with the EU.

In January, the prime minister said the UK should consider “even closer alignment” with the single market, which was preferable to a customs union. “If it’s in our national interest … then we should consider that, we should go that far,” he said.

Concerns were raised at the European parliament on Thursday over EU citizens in the UK and British citizens in Europe post Brexit. MEPs heard about worries over the rights of children born to EU citizens in the UK but who did not know they had to apply for settled status.

They could face charges from the NHS or questions about employability in future, the parliament heard. A senior official in the European Commission’s post-withdrawal agreement unit said: “The UK approach has significant consequences for newborn children, resulting in very high healthcare charges.”

The Home Office was also criticised at the European parliament hearing, which it attended, for ending funding for charities assisting vulnerable EU citizens making late applications for settlement.

Settled, one of the charities, will say in a report published next week that it is seeing “hundreds of requests for advice every week”, but it no longer receives funding from the Home Office.

British in Europe, a grassroots coalition that campaigned for the rights of about 1.2 million British people living in the EU in 27 countries, told the parliament it had no funding from the UK. Although it is one of the interlocutors with the European Commission on Brexit, its principals, Fiona Godfrey and Jane Golding, are now working on an unpaid basis.

“We are all here as volunteers,” they said. “We would call on the British government also to fund the work that is needed to be done, for the support of British citizens living in the EU, because that has not been forthcoming.”