The Duchess of Cornwall has thanked thousands of volunteers who will report for duty to help the NHS through the coronavirus crisis.

As more than 750,000 people – three times the original target – signed up to join the “volunteer army”, Camilla checked in on an elderly woman who was self-isolating.

The duchess, who has been reunited with the Prince of Wales after coming out of self-isolation herself, chatted on the phone to Doris Winfield, 85, from Rickmansworth, Hertfordshire, who has spent the last two weeks self-isolating.

Camilla, 72, tested negative for coronavirus, but isolated for 14 days after heir to the throne Charles contracted the Covid-19 illness.

I salute each one of you - and thank you with all my heart

While Ms Winfield has three daughters who she regularly speaks to, she lives alone and misses her friends and the active social life she used to enjoy.

Clarence House said the duchess and Ms Winfield chatted about a number of different things, including how difficult it was being separated from family, but that being able to see them digitally helped enormously.

Camilla said the most difficult thing about being in isolation was not being able to hug her grandchildren.

They also discussed reading and how much they both enjoyed a good book, particularly Agatha Christie.

We talked about life in isolation and shared hobbies, she was very interested in my family and how I was coping without them. It’s really cheered me up

Ms Winfield said the chat with Camilla “meant the world to me”, adding: “I’ve been incredibly lonely over the last couple of weeks and it was wonderful to talk to her.

“We talked about life in isolation and shared hobbies, she was very interested in my family and how I was coping without them. It’s really cheered me up.”

A photo released by Clarence House shows Camilla sitting at a desk with the phone to her ear.

There is a bookcase behind her, which as well as being packed with books, features family photos of her children and grandchildren, and pictures of dogs and horses.

A sign can be partially seen that appears to say “Welcome to the Nut House” next to a picture of a red squirrel.

Lining the shelves are Harry Potter books, JK Rowling’s The Casual Vacancy novel, books by Peter James, The Mars Room by Rachel Kushner, a white cuddly rabbit, and a mug with a family photo on it.

Empty delivery boxes can be seen on the floor, as well as a wicker basket and a bag, while her desk is adorned with a vase of fresh freesias.

The Royal Voluntary Service, the charity delivering the volunteer effort, will have completed checks for the three quarters of a million applications by the end of Tuesday.

Due to the huge response, the group of vulnerable people they will support in England has now been expanded and they will come to the aid of 2.5 million at-risk people.

Volunteers will be delivering medicines from pharmacies, driving patients to appointments, bringing them home from hospital, making regular phone calls to check on people isolating at home, and transporting medical supplies and equipment for the NHS.

Thousands of approved volunteers will be offered tasks from Tuesday via the GoodSAM app and will start helping people, with more expected to get requests over the coming weeks as referrals ramp up.

Health professionals, pharmacists and local authorities can upload requests for help on the NHS volunteer responders referrer’s portal, and volunteers pick the job they want to do that day and close the task once complete.

Volunteers show themselves as available when their app is switched to “on duty”.

Camilla, president of the Royal Voluntary Service, said: “As the proud president of the Royal Voluntary Service, I wanted to send my warmest thanks to all the NHS volunteer responders who have come forward in unprecedented numbers to offer help to the NHS.

“Royal Voluntary Service has been working with the NHS to recruit people in England who can assist those who are most in need of practical and emotional support at this time.

“Thankfully, the charity has a long and remarkable history of bringing willing volunteers together with the isolated and lonely.

“That experience is needed more than ever in these challenging times.

“And today many more NHS volunteer responders will get in touch with the people they have so kindly offered to help.

“Everyone working in the NHS is under unimaginable pressure day and night in this crisis.

“I feel sure that the presence of so many wonderful volunteers will encourage, as well as support, them.

“I salute each one of you – and thank you with all my heart.”

Health and Social Care Secretary Matt Hancock said: “I want to thank every single person who signed up to be an NHS volunteer responder – their incredible generosity means we can now start helping those most in need across our communities and, in turn, support our heroic NHS staff and social care staff as they continue their outstanding work.

“Coronavirus is one of the greatest challenges our country has faced, and it is truly awe-inspiring to see our whole nation coming together to help each other at this difficult time.”