Pippa Middleton's rumoured wedding dress designer is a risky choice

It's less than 24 hours until Pippa Middleton and James Matthew say "I do" in the society wedding of the year, and speculation is mounting over the bride's dress, ring, flowers and guests.

Today (19 May), the families from both parties – including Carole and Michael Middleton – stopped by the idyllic St Mark's Church in Englefield, Berkshire, for a wedding rehearsal ahead of the nuptials.

The group was also joined by Made in Chelsea star and the groom's younger brother, 27-year-old Spencer Matthews on the rainy day in the English countryside.

Prince George and Princess Charlotte's Spanish nanny, Maria Borrallo, was also spotted descending on the church, though the children, nor their parents the Duke and Duchess of Cambridge, were seen attending the run-through despite the tots being given the big roles as page boy and bridesmaid.

As it stands, 150 guests are said to behold Middleton and Matthews tie the knot – including Prince Harry's girlfriend Meghan Markle, 35. It was previously reported that 33-year-old Middleton lifted the "no ring, no bring" policy for the Suits actress before she landed in the UK on Tuesday.

According to E! news, she was immediately driven from Heathrow to Kensington Palace to join Harry, so it's likely that she has full access to the ceremony and the subsequent reception taking place in a glass palace in the grounds of the nearby Middleton residence.

After Markle attended Tom Inskip's Barbados wedding back in March in a designer floor-length print dress by British fashion designer Erdem, all eyes will be on Markle as well as Pippa at the wedding. It is likely that she will choose another British designer such as Middleton-favourite Jenny Packham or Alexander McQueen.

As for Middleton's dress, it is rumoured that she will wear a custom made design by another British designer, Giles Deacon. This is not confirmed, however, and all will be unveiled by 11.30am tomorrow when she's scheduled to walk down the aisle.

What we can expect is the dress to be a stark contrast from her sister the Duchess of Cambridge's – that elegant, classic, lace, form-fitting V-neck gown by Sarah Burton for Alexander McQueen which was a total game-changer in both the wedding and fashion worlds. Ground-breaking in the subtlest of ways, Deacon might not be able to replicate its sartorial stature without it looking dated in two decades time.

Deacon is an unexpected choice to design Middleton's wedding dress seeing as he has been known to challenge the traditional ideas of womenswear. He often uses wild prints and pop culture references in his designs and was the mastermind behind Abbey Clancy's flamboyant tiered skirt wedding gown in 2011.

The London Fashion Week favourite is no doubt a risk for someone like Middleton – who plays it safe on a daily basis in boucle jackets, blue skinny jeans and ballet pumps. It would be hard to imagine Middleton gleefully looking back at her wedding day snaps wearing a fishtail gown, anyway.

Footballers' weddings aside, Darlington-born Deacon has dressed some of the world's most famous for the red carpet including Cate Blanchett and Sarah Jessica Parker. In November 2016, the couture designer was seen visiting Middleton's £17 million mansion she shares with Matthews in west London carrying an armful of dress bags, sparking rumours that he was the dressmaker.

Other designers that could be in the pipeline include Duchess-favourite (and safer) designers Emilia Wickstead, Eponine London, Erdem, Jenny Packham and Amanda Wakeley.