Primark has long been a staple of UK high streets, luring in shoppers with low-priced clothes, accessories and homeware.

But in its UK and Ireland stores, like-for-like sales – a key metric in the retail industry – were down 3.1% in the year to September, which it attributed to a “weak” consumer environment and fewer people buying winter clothes during last year’s mild autumn.

As online stores like Shein and Vinted continue to attract young shoppers, does Primark face a fight to remain relevant – or is it just fine?

“While the UK clothing market is seeing subdued growth, Primark has significantly underperformed the overall market,” says Tamara Sender-Ceron, an associate director at market-research agency Mintel, adding that it faces “increased competition”.

Some shoppers point out that online marketplaces like Shein and Temu have even lower prices, a huge range of products, and – crucially – home delivery, something Primark lacks.

At Primark’s biggest London store on Oxford Street, which BBC News visited this week, Serena Milius has just popped in with her 12-year-old daughter to look at pyjamas, socks and the new Stranger Things range.

Serena used to do most of her shopping at Primark – until Shein took over.

“Shein’s our main thing,” the 34-year-old finance manager from Tooting, south-west London, says.

She says her wardrobe is now 90% Shein, and goes to Primark for “little bits and bobs” like flipflops, candles, socks and cosmetics dupes.

Others tell the BBC they’d rather splash out on better-quality products. This includes Martha, a 23-year-old student in Leeds, who only shops at Primark for basics like T-shirts, socks, underwear and cotton buds. For other items, she turns to Weekday, Zara and independent shops.

“I like to buy more expensive items that I’m going to wear over the years,” she tells the BBC as she browses clothes in a Primark store with her mum. With Primark, “it’s not always a lasting item,” she says.

The store was busy when the BBC visited on a late Wednesday afternoon, with mainly female shoppers browsing alone or in pairs. Some said they’d gone out of their way to visit, others popping in after finding themselves in the area.

Some say they’re deterred by Primark’s huge, sprawling stores which can sometimes get very busy.

“I do not enjoy shopping in a Primark,” says Abbi Lily, a 24-year-old content creator from near Bournemouth. She describes the experience as “very overwhelming” and “overstimulating” and says it can be “impossible” to find things.

She used to buy most of her clothes from Primark, but feels it isn’t as cheap as it used to be. “They just don’t have the bargains as much anymore,” she says, echoing comments some other shoppers made to the BBC.

Though Abbi sometimes shops at Shein, she’s trying to become more “intentional” with her shopping and buy more second-hand items, including through Vinted and Depop.

A Primark spokesperson told BBC News that 85% of its products were £10 or under, and said it “continually benchmarks” its prices against competitors.

Shein uses AI to identify trends and launch “thousands of new styles daily”, says Ms Sender-Ceron at Mintel.

According to a survey by Mintel in May, 46% of UK women aged 16 to 34 had bought fashion items from Shein in the last 12 months.

It has held pop-up shops in London and this week opened its first permanent physical shop in a department store in Paris, with long queues of people waiting to get their hands on cut-price garments.

“You can buy anything from Shein,” said one shopper waiting in the French capital to visit on its opening day. “It’s such a cool thing for people my age who are struggling in this economy.”

Critics point to the environmental impact of fast fashion and working conditions in its factories. At the Paris launch, protestors gathered outside calling for a boycott of the brand.

With Shein specialising in delivering clothes to your door, Primark does offer click-and-collect services in its nearly 200 UK stores – but not deliveries.

Some high-street retailers have been struggling in the UK, but Primark has largely bucked the trend – it’s closing a store in Dartford, Kent, next year, which reports say will be its first store closure in a decade. It also opened dedicated Primark Home stores in Belfast and Manchester.

Primark relies on its customers shopping in bulk, Mr Stevenson says. “You might be going in for one thing, but you end up buying seven things that you hadn’t really thought about,” he says. This doesn’t happen as much with online shopping, he says.

Would Primark’s sales be boosted if it did offer delivery? Mr Stevenson is sceptical, saying “it doesn’t feel like they’re losing out by not doing that”, but that it could be an option in future.

“If you wanted to buy a couple of things from Primark for £5 each, are you going to pay 50% of that in delivery charge?” he asks. “Because buying £10 of stuff is going to cost me £5 to get it tomorrow.”

Primark’s spokesperson said that its online model was a “deliberate choice to streamline operations and pass the savings directly to customers”.

Though Primark’s like-for-like sales in the UK and Ireland are down, “I absolutely don’t think they’re doing badly,” says Mr Stevenson, the Peel Hunt analyst. Its UK and Ireland market share has grown, according to data from market-research company Kantar.

And its total sales globally in the year to September were up 1% compared to the previous year as it opened more stores in Europe and the US.

For some shoppers, Primark will always have a hold on them. “I absolutely love Primark,” says Khloe Lightholder, a 34-year-old childcare worker from Essex.

She says Primark is “actually quite good quality for the price” and she visits every few months for a couple of hours, usually spending £200 or more on shoes, bags, perfume and homeware. She sets herself a monthly budget, “but every time I go to Primark that budget is out of the window”.

How much of a threat Shein and other budget retailers pose is an ongoing challenge, but it doesn’t feel like Primark’s brown shopping bags will disappear from our high streets any time soon.