Downing Street has insisted that social distancing was observed at a meeting between Boris Johnson and Conservative MPs, despite all attendees being told to self-isolate after one tested positive for Covid-19.

The Prime Minister has said he is “fit and well” after he was instructed in an email from NHS Test and Trace to isolate for 14 days after Lee Anderson, the MP for Ashfield, subsequently fell ill with coronavirus.

Mr Johnson will stay in his Downing Street flat and continue to work from his No 10 office while being “well looked after and served by staff”, his official spokesman said.

The spokesman insisted at a briefing for Westminster journalists on Monday afternoon that social distancing measures were “observed” at the 35-minute meeting on Thursday morning, and said No 10 was a “Covid-secure workplace”.

“We take every possible step to ensure that hand sanitiser is made available to people as soon as they arrive at the building and it is available throughout the building as you travel through it,” he said.

“But as I say, factors such as the length of the meeting meant that it was the advice of Test and Trace that the Prime Minister should self-isolate, and he of course will follow that instruction.”

Asked about a photograph showing Mr Johnson and Mr Anderson standing less than two metres apart at the meeting, the spokesman said: “They are stood side by side, rather than face to face.”

The spokesman also defended the Prime Minister’s decision to hold the meeting in person, saying such meetings are allowed under the current coronavirus restrictions.

Five other Tory MPs – Andy Carter (Warrington South), Katherine Fletcher (South Ribble), Brendan Clarke-Smith (Bassetlaw), Chris Clarkson (Heywood and Middleton) and Lia Nici (Great Grimsby) – plus two political aides were also in attendance and are isolating.

Jacob Young (Redcar), Maria Miller (Basingstoke), Marco Longhi (Dudley North) and Matt Vickers (Stockton South) have said they too are self-isolating, while Kieran Mullan (Crewe and Nantwich) has reportedly been contacted by test and trace. It is not known if they each came into contact with Mr Anderson.

Mr Johnson told Downing Street staff in a virtual address on Monday morning that he is “fit and well” and said the ambition of the Government was “absolutely undimmed and, if anything, growing the whole time”.

And in a video message posted on Twitter, Mr Johnson – who was admitted to intensive care with coronavirus in April – said he was “in good health”, has “no symptoms” and would continue to “lead on our response to the virus & our plans to #BuildBackBetter”.

He said he would have “plenty more to say by Zoom and other means of electronic communication” as he looks to move on from a tumultuous past week at the top of Government.

The Prime Minister had planned to start the week by relaunching his premiership after days of infighting which led to the exit of his top adviser Dominic Cummings and communications director Lee Cain.

On Sunday night, Downing Street said Mr Johnson would present a committed policy launch on social justice, “levelling up” and coronavirus over the coming weeks which would send a “clear signal of his ongoing ambitions for the United Kingdom”.

It is also a pivotal week for Brexit, as negotiations with the EU reach their final phase.

The Prime Minister had been expected to lead a No 10 press conference on Monday evening, but Health Secretary Matt Hancock will host it in his absence.

Downing Street hopes, however, that Mr Johnson will be able to take part in Wednesday’s Prime Minister’s Questions session in the House of Commons virtually.

His spokesman said: “Our firm intention is that that will happen but we are just speaking with the parliamentary authorities on the details.”

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

In his Twitter message, 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.”

Mr Johnson’s official spokesman confirmed that the Prime Minister had had at least one coronavirus antibody test after he fell seriously ill with the virus during the first wave of the pandemic.