The Foreign, Commonwealth and Development Office (FCDO) updated its guidance for travel to France and Spain last week.
It now says that anybody visiting those countries without a hotel or other accommodation booked may need to provide proof that they have somewhere to stay. Holidaymakers staying with friends or family could find that their hosts need to provide them with an official document from the local authorities.
In France this is called the 'attestation d'accueil' (accommodation certificate) and costs u20ac30. The Spanish equivalent is called the u201ccarta de invitaciu00f3nu201d and costs u20ac78.
People visiting second homes in France will have to provide proof of address, such as a utility bill.
However, the Spanish government has told Which? that travellers won't be asked to prove they have accommodation booked.
A 2006 European directive allowed national governments to require this kind of proof of accommodation for visitors from outside the EU. It's only since the Brexit transition ended on 31 December last year that these rules apply to British travellers.
However, member states were allowed to opt in or opt out of the requirement for travellers to prove they have accommodation booked when staying with friends or family. The FCDO pages for Portugal, Italy and Greece make no reference to British travellers needing to provide this proof.
For most holidaymakers the rules are fairly simple. You'll need to make sure you have proof of a hotel or other accommodation booking when you arrive at border control, just as you would when travelling to the United States. Second-home owners also have to carry proof of address. There's no guarantee that you'll be asked to show it but it is possible.
However, if you are staying with friends or family who live in France it might be more complicated. It will be difficult to prove to a border guard that you have a place to stay and it's within their rights to refuse you entry to the country if not.
In France, people hosting visitors from outside the EU must apply to their local townhall for an accommodation certificate. This certifies that they will take responsibility for the expenses of the visitor while they're in France.
In theory the rules are similar for trips to Spain. However the country is keen to welcome tourists and a representative of the Ministry of External Affairs told us that for British visitors: 'There is no need to provide proof of address or a 'carta de invitaciu00f3n'
Despite this it's clear that border forces in the European Union do have the right to request proof that you have a return flight booked, accommodation and sufficient money to maintain yourself during your stay.
Until travel on a large scale begins again it will be unclear whether some British travellers are asked to provide this kind of proof when visiting European countries.
While it seems implausible for major tourist destinations to check the accommodation documents of millions of holidaymakers, it's clear that border guards now have more discretion to refuse entry.
British visitors would be advised to do everything they can to ensure that they have the correct documentation before travel. There have already been reports of visitors to the UK from EU countries, including Spain, after failing to prove their visit is legal.
The same discretion will also apply to Spanish and other border guards now welcoming visitors from UK.
We asked Frontex, the European Union border agency, whether the new rules are likely to be enforced for British visitors but it told us that it was a matter for national governments.
We have also contacted the French national authorities to ask whether they will be enforcing the new rules.
Spain remains on the UK's amber list and the government has said that British people should not yet travel there unless it is essential.
The rules now say that British visitors, like those from other non-EU countries, can now be asked to show a return or onward ticket and provide proof that they have enough money for their stay. They may also be required to show that they have insurance.