M&M'S London Halloween Candy Shop: Four Floors Open to 11pm

M&M'S London, at 1 Swiss Court on the north side of Leicester Square, W1D 6AP, is the closest thing the West End has to a Halloween candy shop that stays open after the theatres empty. The store keeps hours of 10am to 11pm Monday to Saturday and noon to 6pm on Sunday, and its four floors include a chocolate wall with more than 100 M&M'S selections to scoop.

Size is the point here. The brand's own store page calls it the world's largest candy store, at 35,000 square feet, and you feel that on the escalators: each level has its own colour story, merchandise mix and photo stops. Most people arrive from Leicester Square station on the Piccadilly and Northern lines, a two-minute walk away, or wander over from Piccadilly Circus after dinner.

The building has a past that explains its address. Before the store, the corner was home to the Swiss Centre, a 1960s block that gave Swiss Court its name. After Westminster's regeneration of Leicester Square, the redeveloped site was let to Mars, and M&M'S World London opened to the public on 13 June 2011, the first M&M'S store in Europe. It has since been renamed simply M&M'S London, matching sister stores in New York, Shanghai and Berlin.

Inside, the tone is a theme park more than a sweet shop. Large-scale versions of the red, yellow, green, blue, orange and brown characters appear on every floor, alongside London-themed souvenirs and gift tins. That makes it a very different stop from an old-fashioned jar shop like Mr Simms, and it explains why groups of school-holiday families, couples killing time before a show and tourists hunting for gifts all end up queuing at the same tills.

The chocolate wall is the reason to come. Rows of clear tubes are filled with M&M'S in different flavours and colour blends, and you fill a bag yourself, which means you can build a ghoulish mix from orange, brown and dark shades without paying for a pre-packed gift. Read the labels on each tube before you pull the lever, and pace yourself, because the bags are priced by weight and fill faster than you think.

The second big draw is personalisation. The store page says guests can print their own faces on M&M'S Milk Chocolate candies, which turns a Halloween costume into an edible souvenir if you come dressed up. Ask staff at the printing counter how long the wait is before you browse, so the order prints while you look around the upper floors instead of making you stand at the counter.

If you would rather order ahead, the British M&M'S website runs a Halloween range with ghosts, zombies, pumpkins and mummies printed on the candy. Its online prices include a 40 g cone at £3.20 each, a 40 g small bag at £3.00 each, a personalised 1.5 kg bulk bag at £75.00 and a 1.5 kg bulk bag with 30 plastic pots to fill at £105.00, which is the party-sized option for a classroom or an office treat table.

Timing matters more here than at almost any sweet shop in London. Saturday afternoons in October bring school-holiday crowds, and the escalators become a slow conveyor belt. The quietest window is usually a weekday right at the 10am start, before coach groups and theatre matinee crowds arrive. The other good slot is late: Monday to Saturday the store trades until 11pm, so a visit after a 7.30pm show lets you see the wall without a crush.

Sunday is the exception. English trading rules cap large shops at six hours on Sundays, which is why the store runs from noon to 6pm that day, and those six hours tend to be packed from the moment the doors open. If you only have a Sunday, arrive at noon sharp, head upstairs first, and work your way down to the tills, where queues build fastest late in the afternoon.

Be honest about the merchandise. Much of the floor space is given to plush toys, mugs, T-shirts and London-branded tins, and those are the slowest-moving queues in the building. If your goal is Halloween candy, skip the souvenir aisles, fill one bag at the chocolate wall, add a personalised print if the wait is short, and leave. Anyone looking for unusual flavours rather than one brand will get more variety elsewhere in the neighbourhood.

That alternative is close by. Japan Centre on Panton Street, a few minutes south-west of the square, sells Japanese sweets and snacks, including Hi-Chew chews, which make a good contrast to a bag of M&M'S. If the queue at Swiss Court snakes back past the escalators for more than fifteen minutes, it is a better use of the evening, and you can always come back after 9pm when the families have gone home.

Leicester Square itself is worth ten minutes. The central garden has a statue of Shakespeare and, in the paving around it, a set of bronze statues of film characters added for the square's cinema history. The large cinemas on the east and north sides host premieres, so evenings with red carpets bring barriers and extra crowds. Check the square as you arrive; a premiere night can make the walk to Swiss Court slower than usual.

From the store, Gerrard Street and the gates of Chinatown are a two-minute walk north-east. The bakeries there sell egg tarts and buns, and the restaurants stay busy late, which suits a post-candy dinner. Walk south instead and you reach Trafalgar Square and the National Gallery, which has free general admission, in under ten minutes, making an easy loop through the West End before heading back to the Underground.

Address: M&M'S London, 1 Swiss Court, Leicester Square, London W1D 6AP. Opening hours on the official store page: Monday to Saturday 10am to 11pm, Sunday 12pm to 6pm. Nearest Underground: Leicester Square on the Piccadilly and Northern lines, with Piccadilly Circus also close. The store is spread over four floors with escalators between them, so plan time for each level.

Budget tips: chocolate wall bags are priced by weight, so fill a small bag first and top it up rather than over-filling at the start. Halloween prints are an online range on the official British website, with 40 g cones at £3.20 and small bags at £3.00, and the bulk party bags start at £75.00. Come in costume for photos at the character statues, and keep coats and bags close, because Leicester Square is busy every evening.