The fashion police were out in force today to enforce the new dress code at Royal Ascot.
Dressed in smart purple outfits and carrying hampers containing pink, turquoise or white fascinators - for uncovered heads - and pashmina-type shawls - for bare shoulders - as well as a selection of ties, they patrolled the entrance to the Berkshire racecourse.
If anyone was spotted flouting the regulations, which have been tightened up this year, they were discretely taken to one side and given an accessory for free.
Alternatively, women could select a hat to hire for a £50 deposit, which were displayed in an office next to the main entrance.
Jenny Middlemass, from Royston, Hertfordshire, had not realised she would need a hat to go with her black and cream outfit.
Mrs Middlemass, part-owner of Polski Max which was racing in the 5.35pm Windsor Castle Stakes, said: "I'd only found out on Saturday that I was coming here and hadn't realised I would be going through the Royal Enclosure to get to the owners and trainers area - and would need a hat.
"It's not something I keep in my cupboard.
"I think it's lovely they're doing this though."
She was happy with the black and cream hat she came out with as it matched her outfit perfectly.
"It's £50 I can't put on horses, so I might end up saving some money," the 60-year-old joked.
Her partner David Crossley also had to hire a top hat.
The new rules state that in the royal enclosure, fascinators - which are often favoured by the Duchess of Cambridge - are no longer deemed acceptable. In the grandstand area, headpieces and fascinators are allowed however.
Women are also expected to wear skirts or dresses of "modest length" which fall just above the knee or longer. This clarifies previous guidance which stated miniskirts were "considered unsuitable".
Men now have to wear a suit and tie in the grandstand and black or grey morning dress in the royal enclosure.
The new dress code was announced in January, with style guides distributed to all badge and ticket holders.
The dress code assistants, as their badges read, made a bee-line for Anneka Tanaka-Svenska who was wearing a strapless short white dress with pantaloon trousers by HMH Couture and an elaborate bird cage-style hat.
It was not clear if she was taken to one side for her dress being too short or because her shoulders were bare. Luckily she had a spare outfit to change into.
Mrs Tanaka-Svenska, accompanied by Louis Mariette, who created her headpiece, said: "The dress code has always been quite strict but we always bend the rules slightly - they know us here.
"I always turn up with the biggest hat. And at least this one is covering my head."
Many women chose a red, white and blue theme to mark the Diamond Jubilee.
Jackie St Clair, a former girlfriend of music mogul Simon Cowell, went one step further and wore a headpiece made from a giant Union Jack bow, created by Siggi at Harrods.
Bollywood actress Sofia Hayat accessorised her outfit with sparkly Union Jack-painted nails.
And one group of 16 friends from Cheltenham, Gloucestershire, all coordinated with each other in shades of red, white and blue.
Nicki Green, 48, who decided on the theme, said: "We did the colours for the Jubilee and the Olympics. We've been to Ascot 10 times now and always have a colour theme.
"It was an easy one to pick this year."
Royal Ascot has honoured the Queen by re-naming a race to mark the monarch's 60-year reign.
The Diamond, formerly Golden, Jubilee Stakes, will be run on Saturday - the last day of the sporting event.
The racecourse has been decorated with four kilometres of bunting to add to the occasion, with a 1950s-style street party taking place in the Silver Ring area. Over the week, 80,000 Union Jack flags are being handed out to racegoers watching the royal procession.
Stars of the sporting world spending a day at the races included Gary Lineker, accompanied by wife Danielle, fresh from his Euro 2012 presenting duties.
Footballer Michael Owen, former England goalkeeper David Seaman and former athlete Sally Gunnell were also among the racing fans attending the first day of this year's meet.
Entertainer Russ Abbot, attending with wife Trish, said: "It's a great day out. It's a lovely social occasion - though not necessarily a winning occasion!
"The fact it's a Jubilee year makes it extra special."
Lydia Bright of The Only Way is Essex, wearing a red Hybrid dress and a Beth Hirst headpiece in red, white and blue, said: "It's my first time at Ascot so I'm very excited. We're in an amazing box. I'm going to be putting some money on but I've not got a clue about gambling - I'm going to tell my mum to stop me at £200."
About 300,000 race-goers are expected to attend the sporting and social event over the coming days.