Millions of holidaymakers are set to defy government orders not to travel to “amber list” countries despite warnings that trips should only be made in exceptional circumstances.

Boris Johnson has been told to expect a flood of bookings if the EU opens its doors to fully vaccinated Britons without the need for Covid-19 tests or quarantine – a decision expected this week – amid mounting confusion over the rules.

The Independent calculates 5 million UK holidaymakers are booked to travel abroad to “amber list” destinations for the summer, which includes France, Greece, Spain and other holiday hotspots.

The travel industry has already reported a boom in bookings following the lifting of restrictions on international travel which came into effect on Monday.

“The British government will need to respond because the British people will know that, from Europe’s perspective, they’re allowed to travel there,” said Irene Hays, the boss of Hays Travel, the UK’s largest independent travel agent.

The firm had experienced a 177 per cent boom in inquiries to amber list destinations in recent days – and expected many more “as soon as people have got the advice that they can take those holidays”.

The warning came as the travel industry and opposition MPs united in attacking what Labour called the “dangerous chaos” over what the new traffic light rules mean.

George Eustice, the environment secretary, said trips to “visit family or friends” were permitted to amber list countries – including Mediterranean sunspots Greece, France, Spain and Italy.

But, within hours, he was humiliated by Mr Johnson, who insisted they were “not somewhere you should be going on holiday”, other than for “some pressing family or urgent business reason”.

Lord Bethell, a health minister, issued an even tougher message, telling peers: “Travelling is dangerous. Travelling is not for this year, please stay in this country.”

However, the government appeared to open the floodgates by dropping £5,000 fines for going abroad when the legal ban was lifted on Monday and replaced with the traffic light system.

Huw Merriman, the Conservative chair of the Commons transport committee, told The Independent: “Confusion reigns.

“What’s the point in bringing in a mechanism, labelling amber countries as ‘moderate risk’ and then, by implication, shading them red by telling passengers they shouldn’t even go?”

Up to 5 million package holidays are believed to have been bought to amber countries this summer, although firm figures are not available.

Meanwhile, there is growing alarm over travellers mingling with people returning from Covid-hit – and “red list” – India, creating a “super spreading risk” at airports, warned one senior MP.

“Keeping people in crowded arrival halls for hours on end, including travellers from red list countries, is irresponsible and undermines the whole purpose of the traffic light system,” said Yvette Cooper, chair of the Home Affairs Committee.

Caroline Lucas, vice-chair of the all-party parliamentary group on coronavirus, also seized on the reports of queues of up to three hours at Heathrow passport control.

They have been partly blamed on a shortage of Border Force officials – despite repeated pleas from airlines and airports for more staff to prevent overcrowding.

“This is an unforgivable failure by the government. Boris Johnson must take responsibility and fix this fiasco at our borders,” Ms Lucas said.

Mr Johnson was left scrambling to try to thwart foreign holidays by threatening tourists with huge fines if they break isolation rules on their return.

“You’ll also have to self-isolate for 10 days when you get back and that period of self-isolation, that period of quarantine, will be enforced with fines of up to £10,000,” he said, on a visit to a London vaccination centre.

“So I think it’s important for people to understand what an amber list country is.”

But the Welsh secretary, Simon Hart, plunged the policy into further confusion by warning people should only go to amber list countries “if it is essential” but suggesting “some people might think a holiday is essential”.

“I can think of a quite a lot of people who do think that, but it’s about common sense we’re good at common sense,” the minister said during an interview on Times Radio.

Karen Dee, chief executive of the Airport Operators’ Association, accused the government of making the rules “confusing for passengers”.

“They’ve been told that it is now legal to travel, but getting advice to say, actually don’t – even if they are in a position to accept all of the testing and the self-isolation that would go with travelling to another country,” she said.

Nick Thomas-Symonds MP, Labour’s shadow home secretary, said: “The Conservatives’ border policies have unravelled into dangerous chaos within a matter of hours since international travel was opened up.”

In his interview, the prime minister also hinted that the public could expect more information about the threat posed to the lifting of domestic restrictions by the Indian variant within “a few more days”.

“I don’t see anything conclusive at the moment to say that we need to deviate from the roadmap,” Mr Johnson said.

Pointing to efforts to understand how transmissible the variant is – and how much it can elude immunity from the vaccine – he added: “I’m afraid we’ve just got a few more days of looking at that data.”