The Queen was back to business, without a face covering, as she carried out her first public engagement outside of a royal residence since the coronavirus pandemic gripped the nation.

The 94-year-old monarch was joined by her grandson the Duke of Cambridge at the Defence Science and Technology Laboratory (Dstl) at Porton Down near Salisbury, meeting scientists providing vital support in the UK’s response to the Covid-19 outbreak.

The Queen remarked on the present Covid-19 situation, saying: “It’s doubling itself again.”

Told it was on the rise and the approach was being evaluated, she added: “Well I suppose it was expected?”

Professor Tim Atkins, who co-ordinated Dstl’s Covid response, replied: “Predicted ma’am, yes.”

The Queen added: “With all these horrible new things…”

Prof Atkins responded: “Absolutely, it’s an emerging new disease.”

The Queen ventured from HMS Bubble – the nickname for her reduced household of staff – for what was her first external engagement in seven months.

She was on good form as she quipped while signing the guest book: “Well it proves we’ve been here, doesn’t it?”

She was dressed in her trademark block colours – a Stewart Parvin old rose cashmere coat and silk dress of autumnal woodland florals with a matching Rachel Trevor Morgan hat – with black gloves and her signature black Launer handbag.

There was also the traditional royal duty – the unveiling of a plaque to officially open the Dstl’s new £30 million Energetics Analysis Centre, used by scientists for counter-terrorist work.

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The Queen at the signing of the visitors’ book (Ben Stansall/PA)

But much had changed in terms of the heightened safety arrangements put in place for the royal engagement.

Neither the monarch nor William was wearing a face covering.

But all 48 people who were due to come into close contact with them were very recently tested for Covid-19 by Dstl beforehand, and all came back negative, and social distancing was carried out during the visit.

Porton Down has pioneered some of the Covid-19 diagnostic testing and so was able to test everyone prior to them coming into contact with the royals.

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A socially distanced greeting for the Queen from Dstl chief executive Gary Aitkenhead at Porton Down (Ben Stansall/PA)

The pressure group Republic criticised the Queen for not wearing a face mask, saying she should have set an example.

Graham Smith, chief executive of the organisation which campaigns for an elected head of state, said: “The Queen should be setting an example.

“I can’t see how this fits with the rules everyone else is expected to follow, so the Palace needs to come up with a rules-compliant explanation.”

Members of the royal family including William, the Duchess of Cambridge, the Prince of Wales and the Duchess of Cornwall, have frequently been seen in face masks or visors during some, but not all, royal engagements, but the Queen is yet to be pictured in one.

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The Duchess of Cornwall wearing a face mask (Andrew Matthews/PA)

Face coverings are required by law in certain indoor settings such as on public transport, in shops and places of worship.

The Government recommends wearing a face covering in indoor places where social distancing may be difficult and where the public come into contact with those they do not normally meet.

Although Kensington Palace declined to comment, it is understood the duke was also tested in order to accompany his grandmother, and was negative.

Second in line to the throne William and the Queen, who previously would have been side by side, kept two metres apart.

The Queen also arrived by helicopter separately from the duke, who travelled by car.

Small groups of those taking part in the royal visit were arranged two metres apart for social distancing, with marks on the floor where they should stand.

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The Queen watches as the Duke of Cambridge signs the visitors’ book (Ben Stansall/PA)

A Buckingham Palace spokeswoman said: “Specific advice has been sought from the medical household and relevant parties, and all necessary precautions taken, working closely with Dstl.”

The Salisbury engagement comes amid a resurgence of the virus, with the country battling a second wave and stricter restrictions in place in some areas.

The royal pair were also introduced to staff involved in the rapid response to the Novichok poisoning attack in Salisbury in 2018.

The Queen was last at an official public engagement outside of a royal residence when she joined the royal family for the Commonwealth Day service at Westminster Abbey on March 9.

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The Queen and William (Ben Stansall/PA)

She was told how Prof Atkins also co-ordinated Porton Down’s rapid response team following the nerve agent attack on Sergei and Yulia Skripal, and now led the Covid team.

“It’s the same sort of thing I suppose, is it?” the Queen asked.

Prof Atkins replied: “Very similar. Slightly different for me as I’m not out on the front line as I was for Salisbury, but very similar for the organisation.”

After privately viewing the Linear Accelerator (Linac), an X-ray machine used for inspecting weapons and munitions, the Queen and William watched an explosive-detection scenario as police sniffer dog Max was tasked with finding explosives in a white van.

The Queen asked: “Is he more interested in the ball or the explosives?”, and smiled when told: “Always the ball.”

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The Queen and William watch Max the police sniffer dog (Ben Stansall/PA)

The Queen knighted Captain Sir Tom Moore for his fundraising in July in the grounds of Windsor Castle, where she also watched a mini socially distanced Trooping the Colour for her official birthday in June.

She spent lockdown at the Berkshire residence for her safety and the summer privately in Balmoral and Sandringham.

The Queen, who is at a greater risk of severe illness from coronavirus because of her age, delivered two rare televised addresses to the nation just weeks apart during the first wave of the pandemic.