The former prime minister hit out at Boris Johnson, saying that global Britain “looks shut for business” with a “chaotic” traffic light system.
Strict travel rules are still in place despite a fast moving vaccination programme that is on course to hit the target of all over-50s fully protected by June 21.
At the start of the week, thousands of holidaymakers were forced to travel back to the UK from Portugal after it was placed on the amber list.
Mrs May, speaking during a general debate on the aviation, travel and tourism industries, said the government has failed to act on its promise from June 2020 to get internationally agreed standard health measures in place.
The backbencher said: “One year on, we are no further forward – indeed, what we have is a devastated industry, jobs lost and global Britain shut for business. More than not being any further forward, we’ve gone backwards.
“We now have over 50 per cent of the adult population vaccinated – a wonderful programme – yet we’re more restricted on travel than we were last year.
“In 2020, I went to Switzerland in August, South Korea in September, there was no vaccine and travel was possible – this year there is a vaccine, travel is not possible. I really don’t understand the stance the government is taking.”
Currently, people arriving in the UK from a green list country are not required to self-isolate, while arrivals from amber countries – including France, Spain and Italy – must quarantine at home for 10 days.
Travellers from red list countries must quarantine in a government-approved hotel for ten days at a personal cost of £1,750.
Countries are added to the red list based on vaccination rates and case numbers.
Mrs May raised questions over the “mixed” messaging about travel to amber list countries, adding the system is “chaotic”.
She also told the House of Commons: “I think there are some facts the government needs to be upfront with the British people about and ministers need to think a bit more of when making these decisions.
“First, we will not eradicate Covid-19 from the UK. There will not be a time when we can say that there will never be another case of Covid-19 in this country.
“Secondly, variants will keep on coming. There will be new variants every year. If the government’s position is that we cannot open up travel until there are no new variants elsewhere in the world then we will never be able to travel abroad ever again.
“And the third fact that the government needs to state much more clearly is that sadly people will die from Covid here in the UK in the future, as 10,000 to 20,000 people do every year from flu.”
Mrs May warned that the government “needs to decide whether it wants an airline industry and aviation sector” in the UK, adding: “It is incomprehensible that one of the most heavily vaccinated countries in the world is one that is most reluctant to give its citizens the freedoms those vaccinations should support.”
Boris Johnson is slated to give an update on the final stage of England’s lockdown easing on Monday.