Europeans visiting the UK need to buy an electronic travel authorisation (ETA) before they leave under new rules that came into force on Wednesday.

The ETA costs £10 (€12) and is valid for two years for stays of up to six months at a time. On April 9 the cost is going up to £16 (€19.20).

The rules apply to all foreign nationals who do not already need a visa or have immigration status. UK passport holders and residents do not need an ETA.

The quickest way to apply is by downloading the ETA app or through the government website. Other websites are offering to arrange ETAs for much higher fees, but the government has warned that they will not process applications any faster.

The UK government said most applications are approved within minutes, so travellers can still make last-minute arrangements at the port, airport or train station. However, it advises people to allow three working days in case their application needs to be reviewed.

“You must apply for an ETA before you travel to the UK. You can travel to the UK while waiting for a decision,” the government website says.

All passengers, including babies, will need to apply for an ETA. The permit is valid for two years or until the holder’s passport expires.

There is no limit on how many trips people can make to the UK with a valid ETA, but they will need a visa to stay for longer than six months.