Out and about again: Queen Elizabeth in visit with William

Queen Elizabeth II on Thursday carried out her first public engagement outside of a royal residence since early March when the coronavirus pandemic started to impact upon on all aspects of day-to-day life in the UK

The 94-year-old monarch was joined by her grandson Prince William at the Defence Science and Technology Laboratory at Porton Down near Salisbury, in southern England, and met with scientists battling the virus.

The queen unveiled a plaque to officially open the new 30 million-pound ($39 million) Energetics Analysis Centre, used by scientists for counter-terrorist work. The royal pair were also introduced to staff involved in the rapid response to the Novichok poisoning attack on former Russian spy Sergei Skripal and his daughter in Salisbury in 2018.

Though the UK is in the midst of a resurgence of the virus, neither the queen nor William were seen donning a face covering but both observed social distancing rules of staying 2 meters (6.5 feet) apart from each other and anyone else. The queen had arrived by helicopter separately from the Duke of Cambridge, who had travelled by car.

A spokesman for the palace said all advice was followed.

All 48 people who were due to come into close contact with the royal pair had been tested for the coronavirus. All the tests came back negative.

Kensington Palace, the London residence of William, declined to comment as to whether the prince had also been required to have a test in order to be able to accompany his grandmother at Thursday's event.

The queen's last official public engagement outside of a royal residence was on March 9 when she joined the royal family for the Commonwealth Day service at Westminster Abbey. Before the UK was put into full lockdown on March 23, the queen and her husband, Prince Philip, moved to Windsor Castle, which is around 25 miles (40 kms) west of London.

They spent a large chunk of the past few months at the royal residence of Balmoral in Scotland, before they moved to Sandringham in eastern England. The queen returned last week to Windsor Castle to resume audiences and small engagements, while Philip, 99, has stayed at Sandringham.

Though living a far more solitary existence, over the past few months, the queen has been a visible presence, most notably in her two televised addresses to the nation from Windsor Castle in April and May, which were partly intended to bolster people's resolve in the face of the lockdown.

She also knighted in July at Windsor Castle the 100-year-old Captain Sir Tom Moore for his fundraising efforts in the early days of the pandemic.

And she has been seen taking part in her first video conference call to support those caring for others, often in difficult circumstances at home during the pandemic.

On signing the guest book Thursday at Porton Down, the queen quipped: "Well it proves we've been here, doesn't it?"

It's certainly been a while since she could say that.