Britain does not have a proper plan for its 14-day international quarantine and the introduction of such a "useless and ineffective" scheme will do untold damage to the country's tourism industry, the head of Ryanair said on Thursday.

Britain is due to introduce a 14-day quarantine for international arrivals from June 8 to prevent a second surge in the coronavirus pandemic.

"You don't have a quarantine, people are going to be allowed to come in next week through Heathrow and Gatwick, they then get on the London Underground, the trains, the busses, the taxis, to get to their destination. They can stop off at the supermarket, they can play a round of golf," Michael O'Leary told BBC TV.

"This is going to do untold damage to British tourism, the thousands of hotels and restaurants and guest houses all over the UK that depend on European visitors will be deterred by this useless and ineffective quarantine."

(Reporting by Kate Holton; editing by Guy Faulconbridge)