The warning is specifically aimed at travellers heading to Lisbon due to the city hosting World Youth Day.

In a statement, the Foreign Office says: “Portugal will host a visit from the Pope as part of World Youth Day from 1-6 August. During this period, you should expect an increase in the number of people using public transport and other facilities in the Lisbon area.

“Be prepared for road closures and restrictions on accessing the city by car on days when major events are taking place. There will be enhanced security checks at land borders from 22 July to 7 August.

“If you are travelling to Portugal by road during this period, you should familiarise yourself with the authorised border crossing points and allow more time to enter/exit Portugal”.