The President of the European Commission has said it will be up to the UK to decide how close or how distant it wants to be from the European Union and also from the single market.
Ursula von der Leyden said it cannot be expected to have no free movement of people and then expect to have free movement for goods, capital or services. She said it was either all four or none of this was possible.
She said there could not be a level playing field with divergence on tax and standards.
Ms Von der Leyen was addressing MEPs at the European Parliament in Strasbourg where Croatia has taken over the presidency.
She said Croatia's presidency came at a crucial time for Brexit.
Following her recent trip to London she told MEPs that behind each of the 3.5 million EU citizens in the UK, there were personal stories and those people were teaching children, treating patients and working on farms and in factories.
Ms Von der Leyen said these people wanted to have peace of mind and a plan for the future and to feel at home in the place they call home.
She said the EU Withdrawal Agreement provided comprehensive rights for these citizens and it was up to the UK to safeguard those rights.
She said many EU citizens living in the UK had already received proof of their right to remain but she said many more had yet to apply, whilst others were confused.
She said there was a need for all citizens, especially the most vulnerable to be protected and added that the EU Commission would be keeping a close and vigilant eye on this issue.
The European Parliament is debating a resolution to address the rights of these citizens, as well as those of UK citizens residing in the EU.
A vote on the issue will take place tomorrow.