But UK bookings lag behind amid shifting Covid travel restrictions, the travel giant says.
Travel giant Tui has said bookings have jumped by 1.5 million since May, primarily driven by bookings from continental Europe.
Tui said pent-up demand from European holidaymakers was behind the rise.
One travel expert said UK bookings were lagging because of “the unpredictability of government advice”.
The UK government has consistently said that travel restrictions are needed as a measure to combat the spread of the Covid pandemic.
Tui and many other firms in the travel sector have been hit very hard by the effects of coronavirus.
The travel firm, which has its headquarters in Hanover, has had a number of bailouts from the German government and loans worth billions of euros.
Because of Brexit, its credit line from a British bank could not be extended beyond summer 2022.
Despite the jump in summer interest, total Tui bookings were still down 68% compared with summer 2019.
Tui said that about 4.2 million customers had booked for summer 2021, with an increase of 1.5 million bookings since May.
But while UK bookings are picking up, they are still lagging behind Germany, Belgium and the Netherlands.
UK customers are normally a major part of Tui’s business, but only about 17% of those 4.2 million summer customers were from the UK.
In the third quarter, only 50,000 customers departed from Tui’s northern region, composed of the UK and Ireland, the Nordic countries, Canada and Russia.
This reflected “limited green list destinations made available by the UK government” and the “stop-start nature of permitted destinations under UK travel restrictions”, Tui added.
Travel expert Simon Calder said: “The simple reason bookings are so sluggish in the UK is the unpredictability of government advice.”
He said international leisure travel from the UK was banned completely for 19 weeks until 17 May, and then holidays were available quarantine-free only to “green list” countries – of which Portugal was the only significant and accessible destination.
“But within three weeks, Portugal was back on the amber list at short notice, triggering a rush to the airports,” he said.
“With similar moves from the Balearic islands of Spain, and Mexico being placed on the ‘red list’ at 78 hours’ notice, I am hearing from a lot of prospective travellers that they are not confident enough to book – and from many of those with bookings that they wish they hadn’t committed,” Mr Calder said.
He said that he was hoping to go “Greek island-hopping” in late August, but was waiting for the next UK travel list review on or about 25 August.
By contrast, there were far fewer government travel restrictions in Germany, Belgium, the Netherlands and Poland, he said, and “crucially no expensive testing for returning vaccinated holidaymakers”.
The UK government has a “traffic light” system in place for international travels, with green, amber and red list countries.
This week, it updated the list, with France moving from “amber-plus” status to normal amber country rules.
Most countries are on the amber list, with adults that have been fully vaccinated in the UK, US and most European countries not having to self-isolate upon arrival in the UK.
The UK government has previously said that while it wants people to be able to travel, the travel lists are updated “to protect us against new variants” of Covid.
The Department for Transport was approached for comment.