Boris Johnson is set to challenge Angela Merkel over why she pushed for tougher restrictions on vaccinated British travellers when they hold talks at Chequers on Friday.

The Prime Minister and the German chancellor are expected to discuss travel rules during the pandemic when they meet at Mr Johnson’s official country residence.

Mrs Merkel recently called on the European Union to adopt a single policy of making Britons quarantine even when double-jabbed to protect against the Indian or delta variant of Covid.

But Mr Johnson declared on Thursday that getting two doses of a Covid vaccine would be the "liberator" for travel, repeating that rules for quarantining when arriving in the UK would be loosened later in the summer.

How many people have been vaccinated?

Mrs Merkel’s visit to the UK marks something of an international swansong as she prepares to step down in September after 16 years as chancellor. Ahead of her 22nd and final UK visit as the German leader, a host of announcements around the theme of German-British cooperation were made.

A new award for British and German women in science is being created in honour of Mrs Merkel, who studied the subject, with £10,000 given each year to an astrophysicist. The award is  named after Caroline Herschel, a German-born British astrophysicist who was a pioneer in the field, and the first medal is expected to be awarded in early 2022.

The leaders will announce that the UK and German cabinets, made up of the most senior ministers in each government, will hold an annual joint meeting, starting next year.

Mrs Merkel will address a virtual gathering of the UK Cabinet on Friday, becoming the first foreign leader to do so since Bill Clinton, the former US president, in 1997.

An intention to increase funding for the UK-German Connection, an exchange programme that involved 4,300 participants in 2019, will also be announced.

But the message of joint working risks being overshadowed by differences over how British travellers visiting the EU should be treated once they arrive.

Last month, Mrs Merkel urged fellow EU countries to introduce quarantine for vaccinated Britons given the highly transmissible Indian or delta variant, as Germany has done.

She said: "In our country, if you come from Great Britain you have to go into quarantine – and that’s not the case in every European country, and that’s what I would like to see.”

Where is the Indian (Delta) variant in the UK?

The proposal, if adopted, would have severely curtailed the ability of vaccinated Britons to enjoy holidays when visiting Europe, but it has so far been rejected by other EU nations.

During a press briefing on Thursday, Mr Johnson’s official spokesman suggested the topic would be talked about when the leaders met.

"Whilst I wouldn’t seek to predict what exactly will be discussed, I think it’s fair to say that the PM and Chancellor Merkel will talk about opening international travel for the benefit of both UK and German nationals," the spokesman said.

Mr Johnson also talked up the protections that having two jabs gives from Covid as the Government plans to change its rules to let fully-vaccinated people avoid quarantine when returning to the UK from abroad.

He said: "I’m very confident that the double jabs will be a liberator and they will enable people to travel. We’ll be setting out a lot more about the details of that in the course of July, in the course of the next few days, about how we see it working. But there’s no doubt at all that once you’ve got two jabs you are in a much better position."

On Thursday, there were signs that Germany was preparing to soften its stance on British travellers, as figures showed the Delta variant now accounts for 37 per cent of new Covid cases in the country, up from 15 per cent a week earlier.

Jens Spahn, Germany’s health minister, said if the Delta variant becomes dominant in the country and vaccines are shown to protect well against it, Britain may no longer be considered a so-called coronavirus variant country, from which most travel is banned. 

"If both of these things are confirmed, we will then be able to treat Portugal and the United Kingdom as high-incidence areas", rather than variant countries, he said.

Tony Blair, the former prime minister, backed Mr Johnson’s position with a new paper on Thursday about how to treat fully vaccinated Britons. 

"The data is clear – they’re less likely to get the virus, less likely to transmit it and much less likely to be severely sick," he said. "Germany’s attempt to block UK travellers to Europe even if vaccinated, on the basis of the prevalence of the delta variant, makes no sense when we know the variant is already in Europe and will become the dominant strain there also."