From Wednesday, travellers from the UK aged 12 and above are only permitted to enter Malta if they have had both doses of a coronavirus vaccine.
But authorities in the central Mediterranean archipelago revealed on Monday that they will only accept printed letters sent by the NHS as proof.
That means tourists planning to use the NHS app to demonstrate their status face being turned away at UK airports or the border in Malta, even if they are fully vaccinated.
They are worried about the spread of the Delta variant
Cathy Ward, British High Commissioner to Malta
The UK Government’s website states that letters are expected to take “up to five working days” to be delivered.
Several affected people have sent Twitter messages to the British High Commission for Malta stating that the policy means their trips cannot go ahead as planned.
Mark Holland, of Hove, East Sussex, wrote: “I travel in under three days, and have no time to request a letter.”
Children aged five to 11 can travel if they are accompanying their fully vaccinated parents or legal guardian, and must show evidence of a negative PCR test taken within 72 hours before arrival.
No test is required for those aged under five.
The requirement for UK arrivals for those aged 12 to 17 to be fully vaccinated is effectively an outright ban, as the UK is not vaccinating under-18s.
Katie Crookshank, of London, wrote to the High Commission: “We have a 12-year-old girl who is distraught as she now can’t be a bridesmaid in August.”
She continued: “The reputation of Malta being a family friendly island is being damaged. Why can’t they be PCR tested?”
British High Commissioner to Malta, Cathy Ward, replied that she was “so sorry to hear this”.
She added that the Maltese authorities have said “the guidance on teenagers is due to the virus now spreading fastest in this age group and they are worried about the spread of the Delta variant”.
There was a surge in demand for holidays in Malta, Spain’s Balearic Islands, Portugal’s Madeira and a number of Caribbean destinations after the UK Government announced last week they would be moved to the green travel list on Wednesday at 4am.
The change means people arriving in the UK from those places no longer need to quarantine at home for 10 days.
Price comparison website TravelSupermarket said Malta went from being its 17th most popular country among package holiday customers to number five following the announcement.
A government spokesperson said: “As we continue to cautiously reopen international travel, the NHS COVID Pass will be a key service that allows people to demonstrate their Covid-19 vaccination status.
“Travel advice for Malta has been clear that from 30 June all arrivals from the UK will need to present full proof of vaccination and, for residents in England, only the NHS Covid Pass letter will be accepted.
"We are actively working with the Maltese Government to ensure digital options for proof of vaccine via the NHS App and NHS.UK are accepted as soon as possible to give citizens a full range of options."
In other travel news, family holidays to Portugal are back on after officials dropped its quarantine policy requirement for children.
In a surprising u-turn, the country reversed its decision to make children over 12 isolate for 14 days.
Portugal previously said only those who were double-jabbed would be allowed to enter. This prevented British families from holidaying there because the UK is not vaccinating under 18s.
However, last night the country announced under 18s travelling with a fully vaccinated parent or guardian would be exempt from the rule.
Instead, children aged 12 and over must show proof of a negative Covid test while under 12s are completely exempt.