As the most photographed and filmed woman in history and the longest reigning monarch, the Queen has been a focal point for mass communication as it has evolved, from its early days with the first colour photographs and newsreels, to the arrival of television and the internet. When she came to the throne in 1953, the Queen was just 25, her extraordinary coronation gown, created by Hartnell, was embellished with complex symbols and heraldic emblems of the British Isles and the Commonwealth, including an intricate pattern of Welsh leeks, meticulously embroidered on the dress.

It’s worth noting what a fantastically glamorous figure the young, 20-something Queen cut, and just what an impact her youthful, attractive image made on the national morale and psyche in the early days of her reign. For a country emerging from wartime austerity, the young Elizabeth was a figure of hope and modernity. The fact that she came to the throne during the heyday of British couture worked in her favour, and although she may have not set out to create trends, she was certainly much imitated. There was even a certain adventurousness about some of her tastes, according to de Guitaut: “Some of her hats from the 1950s and ‘60s have been really quite experimental and challenging.”

In the 1950s the Queen was shown incessantly on newsreeld in her Hardy Amies creations (“Reserved, restrained elegance”, as de Guitaut puts it) and Hartnell designs (“More showy and flamboyant.”) It was Hartnell who created the Queen’s stunningly glamorous day dresses of that era, with nipped-in waists and full skirts. And in 1960, for her sister Princess Margaret’s wedding, she sported an immaculate aqua-blue silk taffeta gown with matching bolero jacket and gloves. The net hat was embellished with two blue roses to symbolise Margaret’s second name.

Power dressing

The subliminal language of the Queen’s diplomatic working wardrobe worn on state visits abroad has been similarly thought through, with each outfit incorporating a nod to diplomacy in the shape of an embroidered symbol, insignia or colour scheme, designed to pay a compliment to the host country. On one visit to Australia the Queen wore a dress embroidered with wattle, the national flower of the country; she wore a dress embellished with mayflowers in 1957 on a visit to Nova Scotia; in 1983 her dress was decorated with Californian poppies for a visit to the west coast of the US; closer to home, at the annual Balmoral Ghillies Ball in the late 1960s, the Queen wore an oyster ball dress with tartan sash. Then there is protocol to consider – the Queen has visited the Pope at the Vatican seven times, and has each time worn black, complete with a veil, as any female member of the royal family is required to do.

The royal wardrobe is now largely created by Angela Kelley in the Buckingham Palace workrooms, and the silhouette is a version of the column shift dresses the Queen first wore in the 1960s. The head-to-toe, colour-blocked daywear and matching hats that the monarch favours for her public engagements have become her personal brand. It is an instantly recognisable style.

“It’s a dialogue between designer and Queen, and in a way the Queen’s clothes set her apart from us,” says de Guitaut. “Because if she’s going somewhere we need to see her, otherwise it negates the point of her being there. People want her to stand out. So the format of her dressing has followed a constant path – the day dress and jacket or coat suit and a hat, and the obligatory accessories. You don’t see pattern much. You see a flash of solid, vivid colour with the hat matching the outfit, and the shape of the hat is recognisable.” In a perfect British Bake-off twist, some of the most iconic Royal hats recently inspired a range of cakes by Marks and Spencer to celebrate the 90th birthday of the monarch.

There are rules that are always adhered to – the two-inch heel, the hemline below the knee, the hem weighed down to avoid undignified wardrobe mishaps in windy conditions. The hats are small brimmed and tall (it is rare to see the Queen without any headgear – headscarf, hat or tiara is worn – unless she is indoors). The colours are bold, some might say difficult, pastels - lemon yellow or coral – and the silhouettes are tailored and suity. But it works – so much so, in fact, that the style has become a kind of paradigm for female power dressing, and has been adapted and borrowed over the decades by the likes of Margaret Thatcher, Angela Merkel , Nicola Sturgeon and Hillary Clinton. The look sends a message of power – it says poise, stature, not to be messed with.

Equally iconic is the Queen’s handbag, perhaps the most familiar item in her wardrobe. The bags are created by British brand Launer, and she is said to own 200 of them, all with elongated straps to allow for the necessary hand shaking. There has long been speculation about the bag’s contents. There is always a folded ￡5 note for the church collection on Sundays, some commentators have claimed, and a lipstick and mirror. And a mobile phone, suggest others - to call her grandchildren. The Queen has been said to use her bag to communicate subtly with her staff – if she places her bag on the table at a dinner, for instance, it discreetly semaphores the message that she would like the event to come to an end. In a recent formal family photo, one of the Queen’s small great-granddaughters clutches the large handbag proudly, as if to emphasise - and slightly lampoon - its near-mythic, talismanic status.

When the occasion demands it – for evening or a high state occasion - the Queen has always emerged triumphant in a fully regal ensemble. Her elegant beaded gowns, white fox-fur capes and glittering jewellery complete with tiara are a signature grand combination. The fact that this is a fashionable look this year, (Alexander McQueen, Saint Laurent, Gucci and Valentino have all incorporated a regal touch in their spring/summer collections this year) would seem to suggest that the royal nonagenarian’s ingenious sartorial messaging is still working its magic.