A £3m grant to help UK nationals living in the EU with residency applications has been set up by the government.
Charities and voluntary organisations will be able to use the money to support UK nationals preparing for Brexit with a focus on those who may struggle with the paperwork.
This includes pensioners, disabled people, those in remote areas, and those needing translation help.
About 1.3m UK-born people are resident in the EU.
Foreign Secretary Dominic Raab said the government wanted to help UK nationals be "fully ready for Brexit, whatever the circumstances".
Under the withdrawal deal agreed between Theresa May and the EU, UK nationals would have kept their freedom of movement rights during a transition period.
However the deal was repeatedly rejected by MPs and the UK is currently set to leave the EU on 31 October without a deal.
There is uncertainty about what a no-deal exit would mean for Britons living in the EU but expats are being advised to register as residents of the country in which they live.
The rules on residency - including deadlines for paperwork - vary from country to country.
The European Commission has urged EU countries, in the event of a no deal, to "take a generous approach to the rights of UK citizens in the EU, provided that this approach is reciprocated by the UK".
It says the EU27 "should adopt a pragmatic approach to granting temporary residence status".
The Home Office has said that EU freedom of movement will end immediately after a no-deal Brexit.
However migration experts have suggested this will not be possible without a system to work out who is legally in the country.
The changes to freedom of movement will not directly affect Irish citizens because British and Irish ministers have signed a deal to guarantee free movement for their citizens crossing the Irish border and cross-border access for study and health care.