All care homes will be able to allow visits before Christmas, Health Secretary Matt Hancock has pledged, amid criticism of delays in introducing visitor testing.

Mr Hancock said rapid tests for visitors – currently being trialled in Devon and Cornwall – should allow rollout across England within weeks.

It comes as Prime Minister Boris Johnson uploaded a video to Twitter saying he was “bursting with antibodies” and “fit as a butcher’s dog” despite needing to self-isolate after coming into contact with an infected MP.

And Public Health England’s head of immunisation said at least half the population could need to be vaccinated against Covid-19 to “really see an impact on spread within communities”.

In a round of morning broadcast interviews, Mr Hancock stressed the final decision whether to allow visits rested with individual care homes and local councils, but said: “I hope to have that in place for all care homes by Christmas.”

He listened as one man described how visits to his wife’s care home in Hampshire had been severely restricted, impacting on her dementia.

Speaking on BBC Radio 4’s Today programme, Michael Blakstad told how coronavirus guidelines at his wife Trisha’s care home was making her situation a “nightmare”.

He said his wife’s Alzheimer’s had become “very far advanced” but the only visitors she was allowed were care home staff dressed in personal protective equipment.

Mr Blakstad, who has Parkinson’s, said: “She was always a lively articulate person.

“(Now) she stands, she fidgets, her head is bowed.

“She’s basically got this form of dementia which means she doesn’t like sitting down.

“That makes it a nightmare being in a single room – it is like being stuck in a hotel room for three weeks without being able to go out. It’s just awful.”

Mr Blakstad said the care home was planning to put in a visiting facility that he described as being “rather like a prison”, with Perspex screens from “floor to ceiling” and speakerphones, but only once there were no more Covid cases at the centre.

Responding to the interview, Mr Hancock described the situation as “heartbreaking” and “really difficult”.

He added: “I know this from personal circumstances as well in terms of members of my own family … who are in the same sort of situation. It is very difficult.

“The problem is that we know when this virus gets into care homes, we know that people in care homes are particularly vulnerable to it and it runs rife, and so we both need to protect people from the virus but also do that in as a humane a way as possible, and we know the impact on people’s health, let alone everything else, on not being able to see visitors.”

Mr Hancock said he hoped to have testing for care home visitors in place for all care homes in England “by Christmas”, with the pilot currently taking place in 20 homes.

But he admitted there were challenges given the sector is largely run by the private sector.

Mr Hancock, who is due to host a Downing Street press conference later, said it was “too early” to determine whether the lockdown measures in England would end after December 2.

Asked whether the lockdown would simply be “rebadged” after the deadline, he said: “You tempt me, but it is too early to say I’m afraid.

“We’ve seen in the last week that there is still a very high number of cases but we do absolutely want to come out of this national lockdown.

“That is our goal, everybody has a part to play in making that happen of course, following the social distancing rules and isolating when you need to, which is the critical thing.”

He said one of the main goals now was to use the mass rapid testing rollout to find those who are asymptomatic with the virus.

It comes as the Prime Minister said he was feeling “great” on his first working day in self-isolation after a 35-minute meeting with Tory MP Lee Anderson, who later tested positive for coronavirus.

In a video posted to Twitter the Prime Minister said: “Hi folks, the good news is that NHS Test and Trace is working ever-more efficiently, but the bad news is that they’ve pinged me and I’ve got to self isolate because someone I was in contact with a few days ago has developed Covid.

“It doesn’t matter that we were all doing social distancing, it doesn’t matter that I’m fit as a butcher’s dog, feel great – so many people do in my circumstances.

“And actually it doesn’t matter that I’ve had the disease and I’m bursting with antibodies.

“We’ve got to interrupt the spread of the disease and one of the ways we can do that now is by self isolating for 14 days when contacted by Test and Trace.”

Elsewhere, Dr Mary Ramsey, head of immunisation at Public Health England, said Pfizer’s vaccine would be stored in cold hubs – including hospitals and wholesalers – and then sent to vaccination clinics and GP surgeries.

Asked how many people need to be vaccinated for a vaccine to have any real effect, she told BBC Breakfast those at highest risk – such as the elderly – would be given the vaccine first to prevent serious illness in those groups.

“Later on, if it turns out that the vaccine interrupts transmission then we may give it to a wider group of people,” she added.

“And then we really need to get maybe half the population vaccinated to really see an impact on spread within communities.”

Earlier, the Government announced the UK’s daily coronavirus testing capacity is set to more than double with the opening of two new “megalabs” in early 2021.

The two laboratories, one in Leamington Spa and another in Scotland, will together be able to process up to 600,000 samples a day when operating at full capacity, according to the Department of Health and Social Care (DHSC).

Meanwhile, the UK is set to become the first country to run final-stage trials of a Covid-19 vaccine being developed by a company owned by Johnson and Johnson.

For the two-dose Janssen study, researchers are aiming to recruit around 6,000 UK participants – from a total of 30,000 people globally – at 17 sites across the country.