A record number of people received their Covid-19 vaccine on Friday, with 711,156 doses given to the UK public.

More than half of the UK’s adult population – some 26,853,407 people aged 18 and over – have now received their first jab, government data up to March 19 suggests.

Health secretary Matt Hancock hailed the milestone as a “phenomenal achievement”.

The Department of Health and Social Care (DHSC) said it remains “on track” to offer the vaccine to all over-50s by April 15.

It comes as countries across Europe have had to impose tougher restrictions amid a rise in Covid-19 cases, with UK scientists warning overseas holidays this summer will be “extremely unlikely”.

Boris Johnson was among those to receive his first dose on Friday when he was given the Oxford/AstraZeneca vaccine at St Thomas’ Hospital in central London.

Friday’s record daily total includes both first and second doses across the UK.

Of those, 636,219 were given in England – the highest daily amount since the NHS vaccination programme began, NHS England said.

Hancock said: “Vaccinating over half of all adults is a phenomenal achievement and is testament to the mammoth efforts of the NHS, GPs, volunteers, local authorities and civil servants in every corner of the UK.

“During April, we will continue to vaccinate those most at risk and around 12 million people will receive their second doses as well.

“It is absolutely crucial people come forward as soon as they are eligible. When you get the call, get the jab, because the more people who are vaccinated the safer we will all be.”

Some 2,132,551 people in the UK – around 4% of all adults – have been given their second dose of the vaccine, while almost 95% of people aged 60 and over have received their first jab, the DHSC said.

Meanwhile, experts have warned there could be a third wave of Covid-19 infections in the UK and advised people not to consider overseas holidays when restrictions ease later this year.

Dr Mike Tildesley, a member of the Spi-M modelling group which advises the government, said there was a danger that new variants could jeopardise the vaccination programme later in the year.

The infectious disease expert Dr Tildesley told BBC Radio 4’s Today programme: “I think that international travel this summer is, for the average holidaymaker, sadly I think, extremely unlikely.

“I think we are running a real risk if we do start to have lots of people going overseas in July and August because of the potential for bringing more of these new variants back into the country.

“What is really dangerous is if we jeopardise our vaccination campaign by having these variants where the vaccines don’t work as effectively spreading more rapidly.”

Government sources said the UK needs to be wary of what is happening in Europe “because in the past that has led to a rise here a few weeks later”, although how things will pan out is uncertain.

European countries are seeing pockets of the South African variant, with studies suggesting vaccines work less well against this strain of the virus.

In the UK, hospital admissions and deaths are still coming down due to the effect of vaccines, but there are worries that cases could rise quickly once restrictions are eased.

Professor Andrew Hayward, a member of the Scientific Advisory Group for Emergencies (Sage), said although another wave was “likely” in the UK, the impact could be less deadly than previous ones.

He told Times Radio: “I think another wave is possible. Likely, even.

“I guess the difference is that another wave will cause substantially fewer deaths and hospitalisations because of high levels of vaccination across the sorts of people who would have ended up in hospital or unfortunately dying if they haven’t been vaccinated.

“So the consequences of another wave are less. I think the challenge is of course we don’t know exactly how much less.”

Experts believe there will be an increasing “disconnect” between cases and hospital admissions and deaths going forward, as vaccines work to keep people from dying.

Regarding foreign holidays this summer, government scientists say it is still unclear what will happen, but the risk of importing cases and variants comes from countries with a higher prevalence than the UK.

In Europe, the French government announced that new lockdown restrictions would be imposed on Paris from midnight on Friday due to an increase in cases.

Chancellor Angela Merkel said Germany may need to apply an “emergency break” on relaxing restrictions amid a rise in infections.

Poland began a new three-week lockdown on Saturday, with shops, hotels, cultural and sporting facilities closed.

Countries including France, Germany and Italy have begun restarting their vaccine programmes with the AstraZeneca jab – reversing earlier decisions to suspend them over blood clot concerns.

The rollout of the AstraZeneca coronavirus vaccine will resume in Ireland on Saturday, the Health Service Executive announced.