"Her Majesty is struggling with stiffness in her legs, so the cart is a perfect solution to getting her around. She's been through a lot of physical battles recently with Covid and her back sprain, which would take its toll on anyone — let alone someone who turns 96 next month."
The electric cart was built by Danish firm Garia as part of a tie-up with Mercedes-Benz and is described as putting "many passenger cars to shame".
It has a range of 80km before its battery needs recharging and while she's relaxing on one of the four brown leather seats, the Queen can tuck into treats from its fridge, or check for weather updates and mapping on the tablet-style 10in screen next to the steering wheel.
The buggy has "weather enclosure" doors and windows, so the monarch will be able to use it all year round, and it also has headlights, 14in alloy wheels, a lockable boot, heated windscreen, cup holders and even Bluetooth speakers.
The source added: "The cart is a new addition to the castle, and they all think it's a great idea. It's certainly fit for a Queen and hopefully it will help her fulfil her engagements.
"Everyone wants her to carry on for as long as possible being seen by the public.
"I'm sure the Queen would rather walk to events and carry on as normal, but she is struggling at the moment."
Queen Elizabeth the Queen Mother regularly used a golf buggy to attend events in the years before her death aged 101 in 2002.
