Thousands of EU nationals could inadvertently become illegal residents in the UK after Brexit, a new report warns.
Domestic abuse victims, children and the elderly are among those at risk of losing their right to remain in Britain despite meeting the required criteria to stay, according to experts.
This could be because they struggle to provide documentation and complete a registration process, or do not realise they need to apply to continue living in the UK legally.
The potential gap was highlighted in a paper by the Migration Observatory at the University of Oxford.
Its director, Madeleine Sumption, said: "The Home Office is clearly keen to create a system that is easy and straightforward to use, and most EU citizens should be able to sail through a simplified application process with little difficulty.
"But for a minority of people, the process will be more difficult.
"Many of these are already society's most vulnerable - whether it is because they are socially isolated, have been victims of exploitation, or face personal barriers such as mental health or poverty."
Many people simply won't realise they need to apply, Ms Sumption added.
She said: "We know from other government programmes like child benefit that people often don't apply for something even when it's really in their interests to do so."
Later this year the Home Office will launch an application system for EU nationals seeking to remain in Britain after Brexit.