This article has been updated to report new advice from the UK and the EU.
Here are some of the areas in which travellers and consumers may be affected.
The date of 29 March 2019 mentioned below was the day the UK was due to leave the EU under the Article 50 process. However, the EU has offered to delay Brexit until April 12 or May 22, depending on whether the British parliament approves the negotiated withdrawal deal.
Passports and visas
Under Schengen area rules, British passport holders post-Brexit will be considered third country nationals. The government says they may need six months’ validity remaining on their passports to travel to the vast majority of EU countries — and advises people not to travel unless documents are in order.
UK and Irish citizens can still travel freely between each other’s countries under Common Travel Area (CTA) arrangements.
Britons going to other non-Schengen EU countries (Romania, Bulgaria, Croatia and Cyprus) will need to check the particular nation’s entry requirements.
The European Commission and European Council have proposed that UK travellers should not need a visa to visit the EU for trips of up to 90 days, in a no-deal scenario. This depends on reciprocal treatment, and the British government has said that EU citizens travelling to the UK will not need visas for tourism and “temporary” business activity.
However, the proposal has reportedly got stuck as European Parliament lawmakers rejected wording within it, describing Gibraltar as British "colony" at Spain's behest. Unless the row is resolved, the outcome is uncertain.
From 2021 and whether or not a deal is in place, Britons will need likely need to apply for a visa-waiver under the EU's European travel information and authorisation scheme (ETIAS). The Commission says this will cost €7 for a three-year period. The scheme for all non-EU citizens is aimed at securing Europe's borders.
Britons travelling to the EU are told by the British government that European Health Insurance Cards (EHIC) may no longer be valid after March 29 if there's no Brexit deal. These have entitled UK nationals to medical care in the EU in the event of illness or accidents.
Instead people are advised instead to take out travel insurance including healthcare as they would for a non-EU country, and check the situation in individual EU nations via the UK's health service website.
In the event of no-deal, British drivers are told they may need an International Driving Permit (IDP) "and extra documentation" to drive in the EU and European Economic Area (EEA), apart from in Ireland which does not require an IDP. They should also carry their UK driving licence, vehicle registration documents and may need to display a GB sticker.
There are two types of IDP, and which one you need depends on which country you visit. Drivers planning to go to France and Spain would need both.
The UK government also says drivers of UK registered vehicles will need to carry an insurance Green Card in the EU and EEA — not a requirement for EU members — unless the European Commission decides otherwise.
UK residents involved in road accidents in the EU may no longer be able to make claims via UK-based organisations, and instead may have to bring a claim in the relevant EU country, in the local language. Compensation may not be possible if the accidents is caused by an uninsured or untraced driver.
Britons living in the EU are advised to exchange their UK driving licence for a local EU licence before 29 March. No deal means they may need to take a new driving test in their country of residence.
Arrangements for EU and EEA driving licence holders coming to the UK would not change. EU and EEA licences will still be valid in Britain even if there is no exit deal.
The UK would fall out of the EU pet passport scheme under a no-deal Brexit. The British government advises cat and dog owners to contact their vet at least four months before travel to an EU country. Similar advice is given by the UK vets' professional body the RCVS.
This would be to allow time to comply with rigorous EU anti-rabies measures, including vaccinations and blood tests. Owners would then need to get a health certificate for their animal from a vet, and present it at a designated EU point of entry.
These conditions are based on the assumption that they UK will be treated as an unlisted country after a no-deal Brexit. The UK is seeking talks to become a listed third country, which would mean fewer extra requirements for pet owners.
No changes to current arrangements are planned concerning animals travelling to the UK from the EU — although restrictions would apply for a return to the continent.
Mobile phone and bank charges
The UK government warns it cannot guarantee surcharge-free roaming for those travelling to the EU, after a no-deal Brexit. The costs that EU mobile operators could charge UK operators for providing roaming services would no longer be regulated.
However, the government says it would impose a new monthly roaming cap of £45 (€50). UK and EU operators could still strike deals on roaming arrangements, although different terms and conditions may apply limiting calls, texts and data.
The UK’s four largest mobile phone companies have said they have no plans to change their approach.
Using UK bank cards in the EU may become more expensive, as may using cards in the UK that are issued by providers based in the EU.
Cars approved by UK regulators will no longer be automatically accepted on the EU market, and vice-versa. The vehicle approval system, which relates to safety and environmental standards, applies to manufacturers: motorists can still buy and drive vehicles in the UK and abroad.
The UK plans to accept automatically EU-approved cars and parts for perhaps two years. However, it’s thought that the choice of vehicles may fall if the certificate conversion process on either side brings extra bureaucracy.
Red tape may also affect products like chemicals, as different permits may be needed in the UK and the EU. Drugs companies would also be hit as regulations would no longer apply on a mutual basis.
Exports could be affected as goods from the UK would no longer be covered by common regulations. Under a no-deal Brexit, EU countries may no longer accept UK standards, and businesses will have to meet their national requirements. The paper cites furniture, textiles, bicycles and cooking utensils.
No deal would see the UK fall out of many EU judicial cooperation arrangements, complicating cross-border disputes.
The UK government's paper highlights the impact on family law, where individuals concerned come from the UK and EU countries. This covers areas such as divorce proceedings, maintenance, child arrangements and child abduction cases.
Some areas would see a switch from EU rules to Hague Conventions — but some experts say legal wrangles could become more complicated for many people.
The government’s papers also cover several other areas, from firearms and data protection, to energy supply and satellites and space programmes. Often they are directed at businesses rather than consumers — but a major shake-up for companies would likely have a knock-on effect on individuals.
The government published the first details of its plans and advice for a no-deal Brexit in August.